The special effects technicians were able to create giant drops of water by filling up condoms and dropping them.
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.
Several of the gigantic props (the scissors, nails, and mousetrap for example) were part of the Universal Studio tour for several years.
Richard Matheson's book was written as a series of flashbacks so that you got into the cellar with Scott quickly. Universal insisted on a linear story. They also vetoed key sequences, such as Scott spending the night with the female midget, a drunk homosexual who abuses Scott, a gang of teenagers who terrorise him, and Scott becoming a Peeping Tom secretly spying on a teenage girl baby-sitter. These were obviously rejected as too risqué for 1957!
Orson Welles did the narration for the trailer for this film. He was at Universal working on Touch of Evil (1958)
Scott Carey's closing soliloquy was added to the script by director Jack Arnold.
Included among the "1001 Movies You Must See Before You Die", edited by Steven Schneider.
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.
While the spider in the movie is clearly a tarantula, in Richard Matheson's book, on which this movie is based, the spider Scott Carey battles is a Black Widow.
Scott Carey's cat was played by feline actor Orangey, according to the book "Hollywood Cats".
As Scott shrank, he should have felt colder and colder as his body became too small to retain heat. Most small mammals compensate for this by having fur and excess body fat.
William Schallert ( doctor Arthur ) was the last surviving member of the cast until his death in 2016 .
Charlie (Paul Langton) drives a 1956 Chrysler New Yorker convertible.
Jack Arnold solved the problem of simulating giant drops of falling water by use of a treadmill dropping hundreds of water-filled condoms.
The plot was something new for Universal Pictures, which had to approve a story that did not have a neatly resolved ending. Matheson's novel ends with the character shrinking to infinitesimal size. There is no last-minute rescue; the man keeps shrinking. In spite of these problems, Zugsmith managed to secure a $750,000 budget. At the completion of production, studio executives wanted to change the ending to a happy one with doctors discovering a serum to reverse the shrinking process; director Arnold refused. With the successful Creature from the Black Lagoon (1954) and its sequels to his credit, he was able to convince the studio to agree to a preview. The test audience was startled at the film, but they liked it; the ending was not changed.