CBS Radio Mystery Theater was a radio drama series that encompassed various genres, including horror, science fiction, historical drama, westerns, and comedy. The format of the show was similar to classic radio programs like The Mysterious Traveler and The Whistler, with episodes being introduced by host E. G. Marshall. As with prior Inner Sanctum Mysteries, each episode began and ended with the sound of a creaking door, coupled with Marshall's greeting and sign-off. The series' theme music featured a series of spooky and eerie sounds played by various instruments. Throughout its run, CBS Radio Mystery Theater boasted several notable actors and introduced a new generation of listeners to the world of radio drama.

The show aired on CBS Radio Network affiliates from 1974 to 1982 and was later repeated by the NPR satellite feed in the early 2000s. There were 1,399 original episodes with a total number of broadcasts, including repeats, of 2,969. Each episode was allotted an hour of airtime, typically running for around 45 minutes. E. G. Marshall hosted the show from January 1974 until February 1, 1982, when actress Tammy Grimes took over for the remainder of the series' final season. Himan Brown re-recorded E. G. Marshall's original host segments for NPR's broadcast of the show in the 2000s.

Sources: wikipedia.org, otrcat.com