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 suffering from pneumonia and only had half of one lung (both the other half and the other lung had been removed due to cancer) and his doctors had told him not to travel to Mexico City because of the thin air at its high altitude. All of Karloff's scenes for all four of these films were filmed on a soundstage in Hollywood in 1968 as a result.
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 horror films that were primarily made and released in Mexico in 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 in 1969.
This film was one of a package of four horror films that Boris Karloff starred in as co-productions between Columbia Pictures and Mexico's Azteca Films. After Karloff's death in 1969, Columbia 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 recreates the glory days of 1970s New York City, complete with theatrical release posters, neon signs, naughty businesses, billboards advertising products from the time period, and even a sign celebrating the end of the Vietnam War.