Between 1985 and 1987, Frank Zappa released a pair of mail-order vinyl box sets called Old Masters that contained remastered and restored versions of all of his albums between Freak Out! and Zoot Allures. Each box contained an album of previously unreleased material called a "mystery disc." Although he eventually reworked and remixed a handful of these cuts for subsequent releases, the majority of these recordings were never again released in any form.
Originally released as two MYSTERY DISC LPs, first issued as bonus records to those who purchased Barking Pumpkins' OLD MASTERS vinyl boxed set in the mid-'80s. MYSTERY DISC includes early jams from Zappa's "Studio Z" days in Cucamonga, live performances by early Zappa bands, musical and spoken-word segments by a young Captain Beefheart, rehearsal sessions by the original Mothers Of Invention lineup and part of the score from the low-budget western Run Home Slow.