Information for the occurrence and extent of apoptosis in soft tissue sarcoma (STS) and their clinical implication are limited. In 102 cases of STSs, apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling method and expression of Bcl-2, Bax, MIB-1 and p53 protein was examined immunohistochemically. The apoptotic index of the STSs ranged from 0 to 15% with an average value of 1.9%. The mean values of positive cell staining for Bcl-2, Bax, MIB-1 and p53 protein were 32.1, 40.8, 17.0 and 20.3%, respectively. The extent of apoptosis and expression of Bcl-2 protein were correlated to the histologic types of the tumor. Synovial sarcoma had a significantly higher expression of Bcl-2 protein, and lower incidence of apoptosis. STS underwent apoptosis at a constitutional level. There were no significant relationships between extent of the apoptosis, expression of its regulatory proteins and prognosis of the patients.