The series was cancelled because Darren McGavin asked to be released from his contract. Not only did he become disappointed with the series' scripts, but he ended up exhausted from the rigorous daily shooting schedule (beginning at 3:00 pm until just before sunrise) and his uncredited producing duties. Three scripts were left unproduced. Two of them were adapted into a "Kolchak" series of comic books in 2003.
The series was the inspiration for The X - Files.
Producer Dan Curtis and screenwriter Richard Matheson were both approached by Universal to work on the series. Although they had worked on the original made-for-TV movies, they both turned down the offer (they weren't keen on the "Monster of the Week" formula).
Actor Richard Kiel, before he became best known as the killer "Jaws" in the James Bond movies, was cast in two consecutive episodes as the monster. He first appeared as the Diablero in Bad Medicine (1974) and then as Pere Malfait, the swamp monster, in The Spanish Moss Murders (1974).
Episode 1.15, "Chopper", is the first script that Robert Zemeckis (co-writing with frequent collaborator Bob Gale) sold in Hollywood.