In an attempt to determine whether muscle-derived stem cells are distinct from satellite cells, we investigated whether muscle-derived stem cells could be isolated from the skeletal muscle of Pax7-deficient mice, which have been shown to be devoid of or to contain only a minimal number of satellite cells. Utilizing a technique that separates cells based on their adhesion characteristics (the preplate technique), several distinct populations of muscle-derived cells were isolated. In these mice, the Pax7 gene was knocked out with the insertion of the LacZ gene. One population was both rapidly adhering, LacZ-positive, and displayed a high myogenic index, but was rapidly lost to terminal differentiation when continuously replated. A second population, which persisted over 50 passages, was LacZ-negative and displayed a low myogenic index. Although Pax3 may have acted as a compensatory mechanism for the myogenic commitment of the LacZ-positive cells, the LacZ-negative cells, despite expressing Pax3, required Pax7 transduction to restore their myogenic capacity. We believe that these two populations of myogenic progenitor cells, each endowed with different adhesion characteristics, may help explain the discrepancy in the literature concerning the presence of myogenic cells found in Pax7-deficient mice.