Proliferative activity of soft tissue sarcomas (STS) in 31 cases was estimated by histologic grading, mitotic count, DNA analysis by flow cytometry, and immunohistochemical procedures with monoclonal antibody Ki-67. Aneuploid was found in 12 of 16 cases (75.0%) with Grade 3, and in 4 of 15 cases (26.7%)with Grade 1, 2 (P=0.0121). Tumors with more than 100 Ki-67 positive tumor cells per 10 high power fields (HPF) had a higher rate of aneuploid (81.3%) than those with less than 100 Ki-67 per 10 HPF (26.7%) (P=0.0038). There were significant correlations between Grade and DI (r=0.4901, P=-0.0051), Grade and Ki-67 (r=0.4636, P=0.0086), Ki-67 and DI (r=0.6368, P=-0.0001). The results indicate that DI and reactivity of tumor cells to Ki-67 may reflect proliferative activity and be helpful for clinicians to judge the biological behaviour of tumors more accurately and objectively. Supplementary to the grading of STS, DI and Ki-67 score could be useful as prognostic parameters for clinical investigation of muitimodality therapy for individual patients.