Extracellular alkaline proteinase was isolated from the Bacillus intermedius culture medium. The enzyme was purified by ion-exchange chromatography 200-fold to apparent homogeneity and has a specific activity of 950 u./mg. The proteinase was maximally active at pH 10, 50 degrees C and is stable at pH 6.3-11.0. EDTA, o-phenanthroline or p-chloromercuribenzoate did not affect the enzyme activity, while phenylmethylsulfonyl fluoride inhibited it by 95-97%. It was concluded that the enzyme is subtilisin-like and belongs to the serine proteinase family of Bacilli.