The hot tub was not built properly or chlorinated. Michelle Pfeiffer, her double, and Mel Gibson got skin rashes and splinters from the wood. Production shut down for a few days while Pfeiffer recovered from her rash.
In one scene, Matt LeBlanc appears on the television in a commercial, which was an actual commercial for Heinz ketchup.
Raul Julia, a trained singer, sings a few Spanish songs in the film. Santa Lucia is a traditional Italian song that originated in Naples. Raul Julia sings this during the scene where Mac leaves with Giovanna.
At the time, Robert Towne was going through legal issues with The Two Jakes - Piège pour un privé (1990), the planned sequel to Chinatown (1974), and it ended up severing his friendship with Jack Nicholson (they have apparently since reconciled). Greg and Carlos each have a speech about friendship, that reflects Towne's feelings of betrayal.
Michelle Pfeiffer reportedly did not get along with writer and director Robert Towne. He called her "the most difficult actress I have ever worked with." This was most likely due to Towne's reputed perfectionism, and the fact that Pfeiffer was going through a divorce.