Pierre Boulle, author of the original novel, wrote a screenplay entitled "Planet of the Men" in his native French. It featured a messianic Taylor fourteen years after the events of Planet of the Apes (1968) and involved a human uprising against the apes, following which they revert back to their primal state. The studio obviously chose to ignore his concept and used a new script for the film instead (which did feature an uprising - the chimpanzees against the other apes, but was changed prior to filming, possibly due to the reduced budget).
The only film in the original series of five that does not star Roddy McDowall, who was committed to another project, his sole directorial effort "Tam Lin". Archive footage of McDowall as Cornelius is played at the start, and David Watson plays the character in the film proper. Despite this, McDowall is often pictured on video and DVD packaging for this film. Interestingly, Watson and McDowall appeared together two years earlier in the made-for-television musical "The Legend of Robin Hood" with Watson in the role of Robin Hood and McDowall playing Prince John.
Due to the smaller budget of this film, the vast majority of the extras cast as apes (including the ones sitting close to Zira and Cornelius) wore pullover masks instead of the famous ape make up.
James Franciscus, who had spent most of his career playing doctors and lawyers, so welcomed the opportunity to wear a costume that could best be described as minimal. Franciscus was a natural athlete and keen tennis player, so was in great shape for the shoot.
According to writer Paul Dehn, the idea for the film came about because of the iconic imagery of the first film's climax.