The green slime creatures were played by Japanese children in bulky monster suits.
Many of the background players are American military personnel who were based in Japan at the time.
One of the few credited screenplays for comic book writer Bill Finger, who co-created Batman with Bob Kane.
The original storyline for The Green Slime (1968) originated in Italy, where MGM also had dealings. Years before The Green Slime went into production, MGM had contracted Italian filmmaker Antonio Margheriti to direct what was originally intended to be a series of four television movies about the adventures of a space station called Gamma One. Margheriti's films in the series consisted of The Wild, Wild Planet (1966), The War of the Planets (1966), War Between the Planets (1966) and Snow Devils (1967), all created over a period of three months and released in 1965. MGM was impressed with Margheriti's films and released the four films theatrically. Gamma One producers Walter Manley and Ivan Reiner were eager to take advantage of these films and made The Green Slime as an unofficial fifth entry in the film series. The only connection the film has to Margheriti's films is the space station, re-titled Gamma Three, which has a similar design as the one in Margheriti's films.
This was the first film ever to be featured on the cult TV series Mystery Science Theater 3000 (1988). An edited version of the film appeared on the show's never-aired pilot - The Green Slime (1988)