The original script by Richard Matheson called for Carl Kolchak to be dressed in Bermuda shorts and wearing an Aloha shirt. Actor Darren McGavin said, "That doesn't sound like anyone I know," and elected to use a different wardrobe. While reading up on the character, McGavin noted that Kolchak had been fired from a New York newspaper years before, and thought, "That's it! He hasn't bought a new suit since!" So, Kolchak appeared in a circa 1950s suit.
At the time of its original airing, it was the most widely viewed TV movie, with a 33.2 rating and a 54 share.
A planned third installment in the franchise, 'The Night Killers', was scripted, but ABC opted to develop the TV series instead of continuing the films. The plot had Tony Vincenzo hiring Kolchak to work for him in Honolulu. While there, Kolchak discovers a cover-up involving UFOs, a nuclear power plant and important people being murdered and replaced by androids.
At a test screening, the audience reaction was so positive that producer Dan Curtis regretted not releasing it as a theatrical feature film.
While filming in Las Vegas, producer Dan Curtis was amazed at how oblivious the casino gamblers were to any events going on around them other than gambling. So as a joke one day, actor Barry Atwater (Janos Skorzeny) was asked to walk through the Sahara's casino in full costume and makeup to see if anyone noticed him. He did this for over 40 minutes, and didn't even get a second glance.