Electrophoretically homogeneous proteolytic enzyme with molecular weight 31,500 and pI 3.75 was obtained from a culture medium of Streptomyces 771 by chromatography on N-benzyl chitin adsorbent, subsequent chromatography on CM-cellulose, and preparative isofocusing and chromatography on Sephadex G-75. The enzyme hydrolyzes N-benzoyl-DL-arginine-p-nitroanilide N-benzoyl-DL-lysine-p-nitro-anilide N-benzoyl-DL-arginine ethyl ester, and Na-caseinate. It also exhibits pronounced thrombolytic activity. The activity of the enzyme was suppressed by soya bean inhibitor, but remained unaffected by chelating agents and phenylmethylsulfonyl fluoride. The enzyme was immobilized on aldehyde dextran, and some kinetic parameters of the immobilized enzyme were determined. The thrombolytic activity of native and immobilized enzyme was studied as well.