Although the film was both shot and released in UK theaters and on U.S. TV in color, the U.S. theatrical release prints of it were released in black-and-white in order to save the distributor money on duplicating prints.
Released to many theaters in the U.S. as part of a double feature with another film that was also produced, directed and written by Herbert J. Leder, It! (1967).
The second consecutive year where Dana Andrews would play a mad (or, at least, impatient) scientist; the previous year he starred in the film Crack in the World (1965).
An early film role for Edward Fox, best known in the 1970s and 1980s for playing a British aristocrat type. In this film, he plays "Prisoner no. 3", who is described as the doctor's brother.
The Merton Park railway station seen in this film closed in 1997 and reopened as a Tramlink stop in 2000. The station building has since been converted into a private residence.