This was actually a reworking of a preexisting script. The original plan had been to set the story in New York, where both Kolchak and Vincenzo had wound up after being kicked out of Seattle. Also, the vampire was going to be Skorzeny, last seen in the original movie, mysteriously back from the dead. Then, word arrived that Kolchak had been green-lit for a series, so the story was reworked into its present form.
The house that the real estate agent is showing at the beginning happens to be Ken Franklin's house in Murder by the Book (1971). It was also used in The Most Crucial Game (1972), as well as a number of other Universal productions, including Quincy M.E. (1976), and The Rockford Files (1974).
Suzanne Charny (Catherine Rawlins) does not speak throughout the episode, with the exception of her hissing at her potential victims.
The estate/house where the vampire (Catherine) hides at the end of this episode is also the location of the Cort estate in "The Norliss Tapes" (1973) which is also a Dan Curtis production.
The last episode of the series to show "The Night Stalker" as the name of the series. The first four episodes of the series had "The Night Stalker" as the series title. Beginning with episode #5, all opening credit sequences had the series listed as "Kolchak: The Night Stalker". When the show was syndicated, all episodes had the "Kolchak" title card. When the series was sold on DVD and Blu-ray, all original title cards were restored.