The dilapidated western set used for the ghost town where Mannix is held captive is the same used in A Gathering of Ghosts (1971).
Although Karin mentions that she is 19 years old, Lane Bradbury in real life was 33 years old.
Final credited appearance of Maureen Leeds.
Although it's established that Karin is Johnny's granddaughter, Paul Fix in real life was only 37 years older than Lane Bradbury.