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 Quand la Terre s'entr'ouvrira (1965).
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.
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.