It has long been rumored that a final scene, in which Dr. Xavier screams "I can still see!" was cut by censors. No footage of this is known to exist. However, the movie does end rather abruptly just as Dr. Xavier seems about to say something, and those words would provide a chilling climax to the story. This rumor is false, according to director Roger Corman. In a Q&A session he said this idea was discussed but never filmed.
This film originally had a five-minute prologue about the human senses. This prologue was removed from all post-theatrical prints of the film, and may have been removed from some of the theatrical release prints. This reduced the running time to 79 minutes. The footage still exists.
The final chase scene involving Ray Milland's erratic driving took place on Soledad Canyon Road between the cities of Santa Clarita and Acton in California--the same place where nearly the entire film Duel (1971) was filmed.
The skeletal building seen repeatedly from Dr. Xavier's point of view (in "Spectrarama")was the Department of Water & Power General Office Building in downtown Los Angeles. Construction had begun around 1963 and was completed in 1965.
The partially finished highway Dr. Xavier travels to Las Vegas will be Interstate 15, known as U.S. 91 at the time the picture was made. The shot of the distance sign is at the top of the downgrade leading north to what was then Stateline, Nevada (modern-day Primm).