Orson Welles did the narration for the trailer for this film. He was at Universal working on Touch of Evil
Richard Matheson had originally written a screenplay for the sequel called The Fantastic Shrinking Girl in which Louise Carey begins to shrink herself. Universal had planned to produce it but the project was eventually scrapped.
Scott Carey's cat was played by feline actor Orangey, according to the book "Hollywood Cats".
Scott Carey's closing soliloquy was added to the script by director Jack Arnold.
The special effects technicians were able to create giant drops of water by filling up condoms and dropping them.
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, which was made at Universal the year before this film, and also featured Grant Williams.