You read it here first, folks.  After months of searching, CitySleuth has found the location of the Bellicec Mud Baths.  The only online reference he had dug up was "somewhere on Clement Street," which turns out to be close but not the case.
Then ...  Jack Bellicec (Jeff Goldblum) runs a Mud Baths business with his wife Nancy (Veronica Cartwright).  She greets him as he enters the reception area from the street. 
 
 
  ...  and Now,  the bathhouse scenes were filmed at 5499 California Street at 17th Avenue in the Outer Richmond (map).  Previously the L & E Market, it had been vacant for a couple of years before director Kaufman built a realistic movie set inside the store.  The site has since 1998 been a children’s dance studio, the home of Miss Tilly's Ballet and Theater Arts.
 
 
  Then ...  Jack walks between two rows of massage booths towards the mud baths in the rear.
 
 
  Then ...  He begins to feel very tired and hardly notices the customers soaking in the baths.
 
 
  ...  and Now,  the dance studio’s original space has since been foreshortened by a new rear wall.  When the movie set was built, the massage booths were on this side of the new wall; the mud baths were behind it.
 
 
      Here’s the 17th Avenue side of the building in 2008, similar to how it was when the movie was filmed, compared with the building today.  New apartments have been built next door encroaching into the 5499 California space and onto its roof.  The dotted red lines indicate the position of the dance studio’s interior back wall Then and Now.
 
 
      Jack lies down for a nap.  The movie’s undercurrent of mystery is suddenly jarred into reality when Nancy comes looking for him.  She screams in terror when, in one of the massage booths, she finds a hairy, slimed half-formed creature with Jack’s facial features.  They don’t know it yet but his body is about to be replaced by a look-alike alien.
 
 
  Then ...  She finds Jack and wakes him up, unwittingly thwarting the body snatch.  They call Matthew; as Nancy lets him in, the panning camera reveals two neon ‘BATHS’ signs, one in each of the store’s two front windows on either side of the central doorway (but note that the one on the right behind Matthew was not lit up during this scene - either an oversight or a setup problem).
 
 
  ...  and Now,  the entrance, previously with a double door, now has a single one.  (Painters had erected temporary scaffolding outside on the day CitySleuth took this photo). 
 
 
      When Matthew sees the body he has a dread feeling that Elizabeth, back at her home, may also be at risk.  He finds her there asleep and carries her out, on the way passing another creature, this one with the features of Elizabeth.  For the second time a body snatching has been narrowly averted.
 
 
  Then ...  Kibner joins them all at the mud baths but Jack’s look-alike has vanished.  This shot in the reception area  (the front door is on the right) helped narrow CitySleuth’s search for the location because the windows beyond them meant that it had to be on a street corner.
 
 
  ...  and Now,  the wall on the left, above, has been removed and frosted glass on the side windows provide privacy from passersby.
 
 
  Then ...  An exterior scene filmed in front of the baths revealed more visual clues to the location: the wall detail at the corner behind Matthew, a kerbside power pole to the left and a curved arch at upper far left.   The neon sign which was dark earlier (five images above) is turned on here.  (The matching sign in the other window would be above Nancy’s head but is obscured by the roof of the car).
 
 
  ...  and Now,  the power pole is still there and the corner wall detail is the same.  From here, trees block the view at upper far left of the adjacent space’s window arches corresponding to the curved detail above.
 
  
    
    
        
    
  
  
  
  
    
    
    
    
    
    
    
    
      
      
  Then ...  Allan takes Julie out for a date at a tavern but things get awkward when two bikers spot them and head over.
 
  
  
 
  ... and Now?  Could this have been filmed inside the Hidive bar at Pier 28 on the Embarcadero (map)?  The angled front door with the window next to it on the right matches nicely with the interior view above.
 
  
  
 
  ... and Now?  But the matching view inside the tavern today shows the bar on the other side of the room compared to the movie view above.  For many decades known as the Boondocks, the tavern was remodeled in 2004, which might included repositioning the bar.  Anyone who can shed light on this is asked to add a comment at the bottom of this post or to contact citysleuth@reelsf.com.
 
  
  
 
      As the bikers mercilessly hit on Julie (Joy Bang), totally ignoring our hapless hero, the writing on the lifebuoy on the wall references Pier 28, the location of the Hidive.  (In another shot the full text on the buoy is seen as 'Maries Pier 28').
 
  
  
 
  Then ...  The big guys follow them outside where we get to see the bar’s name  - the Pier Head.  Allan's amusingly puny efforts to 'fight' them gets him nowhere fast but they leave him mostly unscathed after Julie makes a choice - them.  But, to CitySleuth's eye this is a different building than that used for the interior scene.  (Reader Scherrie Barone, daughter of one of the bar’s owners, has added interesting information about the Pier Head in the comments below).
 
  
  
 
      Reader Joe commented below that an episode of the TV series The Streets Of San Francisco was also filmed in 1972 at the Pier Head.   Here we see Michael Douglas’s character walking in; this wider daylight view also reveals its aka name, Manjo’s.  Scenes filmed inside do not match the Play It Again, Sam interiors, further evidence that two separate locations had been used for these bar scenes.
 
  
  
 
  … a vintage aerial ...  The 1972 street directory listed the Pier Head tavern at 780 Embarcadero South, opposite Piers 42 and 44.  The tavern is clearly seen in this 1930s aerial view.
 
  
  
 
   â€¦and Now,  the tavern and Piers 42 and 44 were demolished decades ago.  Embarcadero South was rerouted to link with King Street and the Giants ballpark was built atop Berry Street; the arrow indicates where the Pier Head Tavern used to be.
 
  
  
  
    
    
        
    
  
  
  
  
    
    
    
    
    
    
    
    
      
      
      Matthew takes Elizabeth to meet his psychiatrist friend, Dr. David Kibner, who is signing his new book at a crowded bookstore.  They bump into a friend, Jack Bellicec (Jeff Goldblum), an intense young writer unimpressed with the book.
 
 
  Then ...  The exterior view of the colorful bookstore reveals the location - it was Bookplace Inc. at 50 Clement Street on the corner of 2nd Avenue in the Inner Richmond district (map).  Note the small restaurant along the block, Eats, at 40 Clement Street...
 
 
  ... and Now,  not long after this scene was filmed the bookstore closed and Eats took over the corner location; it's still there today.  Its former space is currently occupied by Shi's Hair Studio.
 
 
      In the bookstore a distraught woman is overheard confronting her husband for not being her husband - he has changed; she thinks he's an impostor.  Kibner (Leonard Nimoy) quickly goes to her and plays down her fears ... "He's still your husband"  ... "Will you trust me?".
 
 
  Then ...  As she leaves, Elizabeth stops her ... " I understand what you are trying to say" ...  and asks her to call her at her office.  She tells Matthew "That man is not her husband ... he is one of them".
 
 
  ... and Now,  there are two pillars just visible amongst the crowd, at top center and top left center, above.  They are seen in Eats restaurant in the matching shot, below.
 
 
  Then ...  At Matthew's urging, they leave the bookstore.  Outside an antiques store across the street Kibner debunks Elizabeth's assertion that her boyfriend has been replaced by somebody else and suggests she is looking for an excuse to get out.  Confused, she reluctantly agrees to think about it.
 
 
  ... and Now,  back then the store was Golden Era Antiques at 15 Clement Street.  The current tenant is the high-end leather goods boutique April In Paris.
 
  
    
    
        
    
  
  
  
  
    
    
    
    
    
    
    
    
      
      
  Then ...  So far it's been three dates, three strikeouts from Linda and Dick's efforts to find a girlfriend for Allan.  Undeterred, Dick takes him to a waterfront restaurant to meet Julie, a girl at his office.  As they pull up the telephoto lens expands a ship berthed at a pier in the background.
 
 
  ... and Now,  this was filmed outside the Spinnaker restaurant at the end of Spinnaker Drive in Sausalito (map); across the water is the Sausalito Ferry Pier.  The ship was the Southern Pacific Railroads' Berkeley, one of the many ferries that plied the bay during the first half of the 20th century.  After retiring from service in 1958 it spent 12 years moored here operating as a gift shop, the Trade Fair.  Below is the pier today, viewed from the same spot, but the Berkeley is no longer there.
 
 
     Here's a vintage postcard of the ferry during its time in Sausalito.
 
 
      In 1973 the 1700 passenger ferryboat, whose proudest moments were spent carrying survivors across to Oakland after the 1906 earthquake, was towed to the Maritime Museum of San Diego.  There, lovingly restored, it continues to be on display to this day.
 
 
  Then ...  But when they enter the restaurant, this is not the Spinnaker - it's the Trident at 558 Bridgeway in Sausalito (map - the Trident is arrowed in red and the Spinnaker in blue.  The ferry pier is equidistant between them).
 
 
  ... and Now,  there have been some changes over the years but the basic interior look and feel remains the same.
 
 
  Then ...  Their view of the bay through floor-to-ceiling windows as they head to the back patio is expansive.  Note the decorative Japanese Torii gate outside at far left.
 
 
  ... and Now,  the windows have since been replaced and restyled.
 
 
  Then ...  Dick spots Julie with friends on the patio and urges Allan, resisting strenuously, to meet her.  (Was the waitress in the diaphanous outfit hired straight from a red-light club on Broadway?)
 
 
  ... and Now,  the Torii gate is no longer there at the far end and the elevated section at near right is now hemmed in by railings.  You'll have to take CitySleuth at his word when he says that the spectacular patio view takes in Belvedere, Angel Island, Alcatraz, the Bay Bridge - east and west, the glorious San Francisco skyline and, from the far end, the hills of Sausalito.
 
 
      Allan nervously thumps the table causing lettuce and croutons to fly all over the place as he once again makes a fool of himself.  Surprisingly Julie, the one in red and white, agrees to a date.  (Stay tuned, this should be good).