While diving, Matt Farrell (Ashley) is kidnapped by Neva Gordon (Pat Woodell) and Steinman (Jan Merlin) and taken to an island where Neva's father Dr. Gordon (Charles Macaulay) is experimenting, trying to make a "super race" by combining humans and animals.

Director Romero had previously produced 1959's Terror Is a Man, closely based on H. G. Wells' The Island of Doctor Moreau, and returned to the same subject matter with The Twilight People, although neither film acknowledged their source material.

[2] The film, which is also known as Island of the Twilight People,[3] was originally made for New World Pictures, then run by Roger Corman and Lawrence Woolner.

Corman, Wollner and actor/producer Ashley had previously worked together on Beast of the Yellow Night, The Big Doll House and The Woman Hunt.

[1] The film was shot by Fredy Conde and edited by Ben Barcelon; Ariston Avelino and Tito Arevalo handled the score.