Ten axonic isolates of Trichomonns uaginolis were subcutaneously injected to the BALB/c mice in order to assess their pathogenicity by means of so-called "mouse assay" method. All the isolates revealed neutral and acid proteinase activities both in their Iysates and in culture media, but the specific activities of both proteinases in the severely pathogenic group were significantly higher than the mildly pathogenic group (p < 0.05). In the SDS-PAGE system in which the electrophoretic gels contained 0.4% gelatin as the substrate, five different handing patterns of trichomonal proteinases were detected, and the patterns were closely related with the pathogenicity of the isolates of T. vosinalis. All five bands might be regarded as cysteine proteinases group in the inhibitor assays. The cytotoxicity of the Iysates of T. vaginalis to the target Chinese hamster ovarian (CHO) cell line was also significantly different according to the pathogenicity of the isolates, and generally lower in the Iysates treated with cysteine proteinase inhibitors than in the control Iysates. In summarizing the results, it might be considered that the proteinases of T.vaginalis showing five electrophoretic banding patterns are closely related with the pathogenicity and cytotoxicity of the isolates of T. voginolis. Key words: Trichomonos voginolis, proteinase, pathogenicity, cytotoxicity. PAGE