This film and the other three horror films that were all in the same package were originally supposed to be filmed entirely in Mexico City, Mexico in 1968. At that time, however, Boris Karloff was 81 years old and in extremely poor health, was suffering from both advanced emphysema and rheumatoid arthritis, only had one-half of one lung that was still functioning (both the other half of it and all of the other lung had already been removed due to lung cancer (Karloff had been a heavy smoker for most of his adult life)) and could only breathe through an oxygen mask that was connected to a mobile oxygen unit. In addition to all of this, his doctors had already told him not to travel to Mexico City because of the thin air at its high altitude. As a final result, all of Karloff's scenes for all four of these films were filmed on a soundstage in Hollywood in 1968 out of necessity.
In the U.S., this film was first shown in Spanish-language theaters before being dubbed in English and sold directly to television.
This film was one of a package of four low budget horror films that were primarily made in Mexico and then released there in May of 1968, with all of Boris Karloff's scenes for all four of them being filmed on a soundstage in Hollywood, also in 1968. It would be Karloff's next-to-last film before his death on February 2, 1969.
This film was one of a package of four low budget horror films that Boris Karloff starred in as co-productions between the United States' Columbia Pictures and Mexico's Azteca Films. After Karloff's death on February 2, 1969, Columbia then sold off its share of all four of the films to a distributor named Horror International.
A theatrical release poster of this film is on display in Ghostbusters (2016) when the villain of that film recreates the glory days of New York City in the 1970s, complete with other theatrical release posters, neon signs, adult businesses, billboards advertising products from the time period and even a sign celebrating the end of the Vietnam War.