Despite the original being a significant success, the budget was slashed for this sequel. It went from five million dollars to 2.5 million dollars in one fell swoop. This was mainly due to 20th Century Fox teetering on the brink of bankruptcy following some majorly expensive failures, such as Hello, Dolly! (1969), Star! (1968) and Tora! Tora! Tora! (1970) The recruiting of Ted Post as director was instrumental here as he was used to minimal budgets and shortened schedules from his work on television.
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.
The only film in the original series of five that does not star Roddy McDowall, who was committed to another project. 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.
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 made this movie instead.
Originally, there was going to be a scene featuring a half-human/half-ape child. However, the producers were afraid that not only would the scene be too confusing, but that they would also lose their "G" rating.
20th Century Fox producer Irwin Allen used the tiled tubular set of subterranean New York City for an episode of Land of the Giants (1968), and as an electrical power-duct in his television movie City Beneath the Sea (1969). In both cases, panels of red lights were inset into the tiled tube making it more useful in these later projects. The same set would be used in Conquest of the Planet of the Apes (1972) as corridors between sections of the Ape Management complex (utilizing white lights).
The 'official' budget is three million dollars. However, director Ted Post stated the budget was 2.5 million dollars. Another historian claims it was 4.7 million dollars. All these discrepancies can be found in the Blu-ray 40 Year Box Set; under special feature documentaries for POTA; Beneath; and Battle.
All five original "Planet of the Apes" movies were number one at the U.S. box-office when released. "Beneath the Planet of the Apes" spent two weeks as the number one top grossing film: the week of May 31, 1970 it made 3,595,936 dollars, and the week of June 7, 1970 it made 3,146,395 dollars.
Several sources (including the official novelization, comic adaptation, and music CD soundtrack), reveal Brent's first name as 'John'. His dying fellow astronaut, called only Skipper, wears a nametag which, when magnified in freeze frame, appears to be Maddon or Maddox. Don Pedro Colley's character is named "Ono Goro" in the script -- Colley was bemused to discover that he was credited as "Negro" in the end titles.
In the next film, "Escape...", it is stated that Dr. Milo raised Taylor's ship from the inland sea where it crashed and sank, and then studied it and learned how to operate it. For the timing to make any sense, Dr. Milo would have had to be working on it during the events of this film.
The name and topographical configuration of the underground subway station are inconsistent. The real "Queensboro Plaza" station in New York City is above ground, serving elevated tracks. The nearby "Queens Plaza" station and tracks are located underground.
The first film in the original film series not to have the 20th Century Fox logo at the beginning of the film. This would become a trademark of the films that would continue for all the following entries in the original film series.
At the end of the 1968 Planet of the Apes film, (and the flashback scenes of Beneath) Taylor rides off with the "black" first movie rifle, with a belly mounted strap. That rifle stock housed a WWII era M-1 carbine which had the front and rear sights removed. In the 1970 sequel, Beneath the Planet of the Apes, Taylor removes the rifle from the rifle scabbard on the saddle, and proceeds to wack the stone wall apparition with the rifle butt, before he falls and disappears. The rifle he uses in that scene now has a redesigned BROWN stock, fitted with a retracted bayonet, .now has an adjustable rear sight (missing in the first movie), and has a shorter side mounted strap/sling. When did he have time to make all of those changes and why?!! ;-)
The trivia items below may give away important plot points.
An alternate ending was written where Taylor, Brent and Nova escape the underground city prior to the detonation of the bomb, which was not a doomsday device as it is in the finished film. They return to Ape City and, along with Zira and Cornelius, release the humans from the cages and a new order is begun. The script ends hundreds of years later with the Lawgiver teaching a group of ape and human children, who sit in harmony together. The final shot of the script shows a mutated gorilla emerging from the underground and fatally shooting a flying dove. (The "Lawgiver Scene" was resurrected as the framing structure for Battle for the Planet of the Apes (1973).)
Charlton Heston was reluctant to reprise the role of George Taylor for this movie. He eventually agreed on condition that his scenes had to be shot within a two week period. He also insisted that Taylor had to be killed. He agreed to a compromise in which he'd disappear in the beginning of the film and reappear to die at the end. Heston claims in the documentary Behind the Planet of the Apes (1998) that he personally suggested the ending, saying, "Why don't I just set off this bomb and destroy the world. That's the end of the sequels."