This production originally began shooting with Jason Robards in the title role(s), and a makeup that was heavily influenced by John Barrymore in the 1920 silent version (Dr. Jekyll and Mr. Hyde (1920)). Production was halted due to a strike, and when filming was able to resume, Robards was no longer available. Jack Palance took over the Jekyll/Hyde role, and the makeup concept was radically changed - inspired, more or less, by that of a satyr.
The majority of background music is the same that was used for Dark Shadows, also produced by Dan Curtis. In fact the music playing when Dr. Jekyll first visits Gwyn Thomas at the pub is Quentin's Theme from Dark Shadows.
During shooting, Jack Palance suffered an on-set accident when he fell during a chase scene and broke his left arm. A careful examination of his last scenes as Hyde will reveal he does all his action with one arm.
There was more makeup on Jack Palance than met the eye: makeup artist Dick Smith "corrected" Palance's broken nose (as Dr. Jekyll), with a small foam latex prosthetic appliance, to give him a more handsome appearance.