Culture filtrate from M. tuberculosis grown in Sauton broth was screened at weekly intervals for elastase and caseinase activity. Both activities were detected concomitantly at 4 weeks and had similar inhibitor and pH profiles. Highest activity occurred between pH 6.5 and pH 7.5. Azocaseinase activity was linear with time between 12 and 28 h at 37 degrees C. Enzymatic activity was inhibited by EDTA, EGTA, dithiothreitol, ethylmaleimide, 1,10-phenanthroline, Zincov, N-tosyl-L-phenylalanine chloromethyl ketone, and N-methoxysuccinyl-Ala-Ala-Pro-Val chloromethyl ketone. SDS-PAGE analysis revealed breakdown of casein after incubation with culture filtrate. These results indicate the presence of a calcium-dependent, elastolytic metalloprotease in stationary phase cultures of M. tuberculosis.