Author Paddy Chayefsky disowned this movie. Even though the dialogue in the screenplay was almost verbatim from his novel, he reportedly objected to the general tone of the film and the shouting of his precious words by the actors, this conflicting with director Ken Russell's typical style of wanting heightened performances. Chayefsky had not seen the film before he took his name off the credits, the script being credited to "Sidney Aaron", a pseudonym for Chayefsky, the two names being Chayefsky's real first and middle names. Russell and Chayefsky fought constantly during production, Russell maintaining that almost nothing was changed from Chayefsky's script and stating that he was "impossible to please".
In a 1981 interview with '"The New York Times", Blair Brown said many of the actors and crew tried out the isolation tank. William Hurt actually hallucinated, while Brown found it very peaceful.
Paddy Chayefsky's novel was partially based on the work of neuroscientist and dolphin researcher John C. Lilly, who invented the isolation tank, and first started taking drugs while "tanking". Lilly's work had inspired Mike Nichols' earlier dolphin movie The Day of the Dolphin (1973). Lilly was an uncredited scientific researcher on both pictures.
William Hurt says that he knew just a little about director Ken Russell prior working with him, and just because he had seen his movies. About his first meeting with Russell, Hurt said in an interview, "We were in this little room and there was this radiator and a little desk and a chair and we didn't sit for a half an hour, neither one of us. Finally he sat on a radiator and I sat on the floor. When he sat on the radiator his pants pulled up and I saw he had Betty Boop socks on. It was then I thought, 'I'll do it'."