In an interview in Fangoria magazine, screenwriter Anthony Harris stated that a good portion of the filmed material was improvised on the set and that the script was ignored.
The enormous success of The Blob (1958) led producer Jack H. Harris to try to do a sequel. Richard Clair had already written a script titled "A Chip Off the Old Blob," but the project had been shelved for many years. In late-1970, Harris' son, Anthony Harris, who had just graduated from USC and was working with a music publishing company, expressed interest in working with his father. Looking for a project, they both agreed on the "Blob" sequel. Larry Hagman, who owned the beach house next door to Harris, mentioned that he had never seen the original The Blob (1958). Harris showed Hagman his personal 16mm print of the film, and he showed such interest, Hagman told Harris he would be able to assemble his friends for the cast, as he felt everyone wanted to be "Blobbed"... but only on the condition he would direct the picture.
The film Godfrey Cambridge is watching on his TV when attacked by the Blob is The Blob (1958). The audio-only tracks are from the film within the film, Dementia (1955), aka "Daughter of Horror", from which stock footage is used in the theater sequences in "The Blob".
Improvisation actor Del Close who appears as 'Hobo Wearing Eyepatch' would later play a much larger role as 'Reverend Meeker' in the 1988 remake of 'The Blob'.
In spite of having a stunt person on set, Robert Walker Jr. lobbied director Larry Hagman to do his own stunts for the rope climbing sequence in the finale. Walker had an acrobatic background, and was allowed to do the stunts.
Harris felt "Beware! The Blob" was too "funny" and not "scary enough" to be successful.
Those annoying clacking balls used in the movie, were an early 70's fad called Kernockers. Later discontinued due to accidental injuries caused when they shattered.
Del Close wears an eye patch in this movie because his cat had scratched his cornea a few days prior to acting in this movie.
This film was reissued in 1982 with a new tagline: "The film that J.R. shot!", as Larry Hagman had gone on to major later success as J.R. Ewing in the TV series Dallas (1978). (The tagline plays on the fact that J.R. was shot in a 1980 cliffhanger.)
While still in production on "Beware! The Blob," writer and producer Anthony Harris was already preparing a sequel called "Curse of the Blob."
When Chester is watching TV, the movie that he is watching is the 1958 film The Blob (1958). At the end of The Blob, the Blob is shipped off to the Arctic. In this movie, Chester tells his wife that his team uncovered the thing in the Arctic.
Del Close later went on to play Reverend Meeker in the 1988 remake of the original Blob.
The only feature film ever directed by actor Larry Hagman, whose only previous efforts in the director's chair were three episodes of I Dream of Jeannie (1965).
The bowling alley featured in the film (the now-closed Grand Central Bowl in Glendale, California) was also used as the exteriors for "Jack Rabbit Slims" in Pulp Fiction (1994).