In very poor health with cancer, Edward G. Robinson was almost totally deaf when he made this movie, and only able to hear anyone if they spoke directly into his ear. Because of this, scenes with him talking to other people had to be shot several times before he got the rhythm of the dialogue and was able to respond to people as if he could really hear them. And because he was unable to hear director Richard Fleischer yell "cut" when a scene went wrong, Robinson would often continue acting out the scene, unaware that shooting had stopped seconds earlier.
The video game in Simonson's apartment, Computer Space (1971), was one of the first coin-operated video games, manufactured by Nutting Associates in 1971 and designed by Nolan Bushnell, who later founded Atari and designed Pong (1972). The video game was painted white for the movie but the original color was either yellow, red or blue.
A sign saying "Green Day" appears in the film. Some people suggest that this is where the rock group got their name from. The font on the store-front window matches that used on Green Day's Uno, Dos, and Tres albums.
Among the buildings in the matte "skyline" in the nighttime background of future New York City in the scene where Gilbert crosses the drainage ditch, one can see the Marina City towers (Chicago) and the Transamerica Pyramid (San Francisco).
According to the book "Future tense: The cinema of science fiction" by John Brosnan, Harry Harrison showed up one day on the set and passed out copies of the source book to the cast and crew. He also gave Edward G. Robinson pointers on his character.
This was the last film shot at MGM Studios back-lot on Overland Blvd. and Culver Blvd. in Culver City, California. The lot was razed in 1973 to make room for an assisted living community and condominiums.
The trivia items below may give away important plot points.
When Thorn discovers that he is too late to stop Sol's suicide, he begins to cry. According to a 1997 interview with Robert Osborne on Turner Classic Movies, Charlton Heston was really crying because he was so moved by Edward G. Robinson's performance. Robinson knew he was dying from cancer and kept it from the cast and crew. He knew this would be his last film, and his death scene was the last scene he ever filmed. He died just ten days after shooting wrapped.
A small, green spirulina-based cracker called "Soylent Green" (officially licensed by MGM) was released in July, 2011. The box does not use any images or characters from the film, but rather attempts (humorously) to be an actual product. The ingredients list does not list "people."
The music which played when Edward G. Robinson was "going home": - The overture was the principal theme from the first movement of Pyotr Ilyich Tchaikovsky's Symphony No. 6, the "Pathetique." - When the visual presentation starts, the music is the first movement of Ludwig van Beethoven's "Symphony #6 (The Pastoral)". - When the flock of sheep appear, the music is "Morning" from Edvard Grieg's "Peer Gynt Suite #1". - At the end of the presentation is "Asas Death", also from the "Peer Gynt Suite".
When Thorn informs the priest in the overcrowded church that Simonson is dead, the priest says, "There should be a requiem Mass, but there's no room. Should I make room?" This is a wink to the source novel "Make Room! Make Room!" by Harry Harrison.