Extracellular elastolytic proteinase was produced by yeast cultures of Histoplasma capsulatum var. duboisii and H. capsulatum var. capsulatum in three different induction media, assayed using elastin-orcein as the substrate. Medium-dependent variations in the time-course for enzyme production were observed and no peak was recorded. The proteinases hydrolysed both casein and bovine serum albumin indicating a broad substrate specificity. Both elastolytic proteinases had similar optimum pH (pH 8) and temperature (35 degrees C); over 90% residual elastolytic activity was measured in the crude enzymes of v. duboisii and v. capsulatum after incubation in the pH ranges 4.5-8.0 and 4.0-7.0 respectively, at 4 degrees C for 24 h. The proteinases were not significantly inhibited by any of the tested proteinase inhibitors. The molecular weights, estimated by column chromatography, were 23 kD. A probable role in the pathogenesis of histoplasmosis is discussed.