Twenty three commercial microbial proteinase preparations derived from various Bacillus or Aspergillus spp. or from Rhizomucor niveus were assessed for proteolytic activity on azocasein at pH 5.5 or 7.0, or specificity on sodium caseinate at pH 5.5 and semi-quantitatively assessed for esterase, lipase, trypsin, chymotrypsin, general aminopeptidase, phosphatase and glycosidase activities using the API-ZYM system. Selected preparations were further assayed for peptidase, esterase and lipase activities at pH 7.0. The proteolytic activity of the Bacillus preparations was greater at pH 7.0, while that of the Aspergillus and Rhizomucor preparations was greater at pH 5.5. All the Bacillus preparations contained one of two main proteolytic activities, thought to be either bacillolysin or subtilisin. Most of the Aspergillus preparations contained the same proteinase, thought to be aspergillopepsin 1, but two preparations appeared to contain a different unidentified proteinase. The proteolytic specificity of the Rhizomucor preparation was different from the Bacillus or Aspergillus preparations; thought to be rhizopuspepsin. According to the results of the API-ZYM system, all preparations contained enzyme activities in addition to their main proteolytic activity, with the Aspergillus and Rhizomucor preparations containing the highest levels and widest range of activities. Generally preparations derived from Aspergillus contained the highest level of general, proline and endopeptidase activities, with the Bacillus preparations conspicuous by the absence of general and proline-specific peptidase activities, while the Rhizomucor niveus preparation contained little or no general or endopeptidase activity. Esterase activity was found in all of the preparations evaluated, with only two Aspergillus preparations containing lipase activity.