The clear culture filtrate from 1-L culture of a laboratory contaminant of Staphylococcus (coagulase- strain, designated Clavelis) was filtered, concentrated, dialyzed, and the proteins were precipitated. The precipitate was washed, concentrated, and aliquoted (about 4 mg of total proteins/ml, designated as ''Stazyme''). The crude preparation was subjected to gel filtration on Sephadex G-75, and the fractions were screened for their lytic ability against Mycobacterium smegmatis. Native proteins in the ''stazyme'' were electrophoretically separated, electroeluted, and their lytic activity against M. smegmatis was compared with parallel controls (partially purified proteins extracted from the same quantity of the uninoculated bacterial growth medium). Only ''stazyme'' preparations caused significant growth inhibition of M. smegmatis, M. chelonae, M. xenopi, M. tuberculosis, and M. kansasii. ''Stazyme'' essentially possessed a lytic activity measured with purified M. smegmatis and Micrococcus lysodeikticus cell walls and showed high bactericidal activity against M. smegmatis, M. chelonae, and M. tuberculosis. It was also able to rapidly lyse intact M. smegmatis organisms, permitting significant yield of mycobacterial DNA.