Organic solvent- and detergent-resistant proteases are important from an industrial viewpoint. However, they have been less frequently reported and only few of them are from actinomycetes. A metalloprotease from Streptomyces olivochromogenes (SOMP) was purified by ion exchange with Poros HQ and gel filtration with Sepharose CL-6B. Apparent molecular mass of the enzyme was estimated to be 51 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gelatin zymography. The activity was optimum at pH 7.5 and 50 A degrees C and stable between pH 7.0 and 10.0. SOMP was stable below 45 A degrees C and Ca2+ increased its thermostability. Ca2+ enhanced while Co2+, Cu2+, Zn2+, Mn2+, and Fe2+ inhibited the activity. Ethylenediaminetetraacetic acid and ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, but not phenylmethylsulfonyl fluoride, aprotinin, and pefabloc SC, significantly suppressed the activity, suggesting that it might be a metalloprotease. Importantly, it is highly resistant against various detergents, organic solvents, and oxidizing agents, and the activity is enhanced by H2O2. The enzyme could be a novel protease based on its origin and peculiar biochemical properties. It may be useful in biotechnological applications especially for organic solvent-based enzymatic synthesis.