Orson Welles did the narration for the trailer for this film. He was at Universal working on Touch of Evil (1958)
The special effects technicians were able to create giant drops of water by filling up condoms and dropping them.
Universal had originally planned a sequel in which Louise Carey also shrinks. The second project was eventually scrapped.
Scott Carey's cat was played by feline actor Orangey, according to the book "Hollywood Cats". Orangey also played the title role in the film Rhubarb (1951).
When Louise is on the telephone, asking the operator for a new unlisted number, the radio is on and the music playing on the radio is the theme song to Written on the Wind (1956), which was made at Universal the year before this film, and also featured Grant Williams.