Vincent Price signed on after reading the first draft of the script. However, the studio demanded re-writes in order to reduce production costs. The re-writes reportedly removed much of what Price liked about the first draft.
It has been erroneously reported that "The corpse shown on the slab in the morgue just before Max Barthold receive visit from the Fly, has six fingers (sic) in his left foot." The left foot has only five toes, but the angle makes the ball of the foot appear as if it may be a sixth toe.
The movie double billed with The Alligator People.
The producers decided that Vincent Price was all they needed, so they hired no other actors from the first movie. Filming was completed in March 1959 for July release.
The script was written specifically to use the standing sets from The Fly.