The monkey was "killed" by being placed in a large set filled with carbon dioxide. When the monkey's cage, containing oxygen was opened, it was rendered unconscious by the CO2. An Assistant director was off camera and brought a breathing apparatus to the monkey who recovered immediately.
Effects footage and props from this film were frequently reused in a number of Universal Studios T.V. shows for more than a decade after its release, including: "The Six Million Dollar Man", "The Bionic Woman", "Knight Rider", and "Airwolf".
The computer error "601" occurs because of a system overload while trying simulate Andromeda's growth and mutation. The error number is a reference to the computer overload error of "1202" (exactly double) which occurred on the LEM during the first lunar descent.
Michael Crichton wrote the rough draft for the novel from which this film is adapted while he was still a medical student. He was inspired after a conversation with one of his teachers about the concept of crystal-based life-forms.
Leavitt, in a protest against inserting something to clean out the GI tract, makes the statement about "risked drowning in that foul bath". The book, but not the movie, had the Wildfire Team submerge completely in an antibiotic solution. The scene may have been cut, but Leavitt still makes reference to it in the movie.
Dr Stone says, "The SDS has arrived, no doubt." when his wife says someone is at the door to see him. The Students for a Democratic Society (SDS) was a college protest group active in the late 1960s to whom Dr Stone alludes.
At the plane crash site, the actor that was supposed to call out, "Major Mancheck," fell out of his trailer and broke his leg. He was replaced on the spot with actor Robert 'Bob' Olen, who did the lines but was never credited for it.
Screenwriter Nelson Gidding broached the idea to director Robert Wise that one of the four scientists should be a woman. Wise initially envisioned Raquel Welch in "Fantastic Voyage" and so objected strenuously to the change. However, after Gidding described in detail the character eventually played by Kate Reid, he convinced Wise that it was a positive addition to the story.