Mystery Disc

Mystery Disc is a compilation album by Frank Zappa. It was released on CD in 1998, compiling tracks that were originally released on two separate vinyl records and included in the mail order Old Masters box sets, which were released in three volumes between 1985 and 1987. (These box sets, issued on Barking Pumpkin, contained repressings of Zappa's albums from Freak Out! (1966) to Zoot Allures (1976), along with a 'Mystery Disc' in boxes one and two.) The CD omits two tracks from the box sets, "Why Don'tcha Do Me Right?" and "Big Leg Emma", both of which were included on the CD version of Absolutely Free (1967).

The recordings featured on Mystery Disc cover the early stages of Zappa's career, and were made between 1962 and 1969 (with the exception of "The Story of Willie the Pimp", a 1972 'field recording'). The material overlaps in places with that of You Can't Do That on Stage Anymore, Vol. 5 (1992), Ahead of Their Time (1993) and The Lost Episodes (1996). A number of the earlier tracks—"I Was a Teen-Age Malt Shop", "The Birth of Captain Beefheart" and "Metal Man Has Won His Wings", all likely recorded in 1964—feature Captain Beefheart on vocals. These are three light-hearted collaborations; "Metal Man Has Won His Wings" has Beefheart reading the lyrics directly from an advert for a comic book.