The aim of the study was to determine the immunohistochemical expression of the PCNA, p53 and bcl-2 proteins in pleomorphic adenomas.onineteen specimens of pleomorphic adenomas were selected for analysis by the streptavidin-biotin-peroxidase method with antibodies againstp53, PCNA and bcl-2 proteins. It was observedweak labeling for p53 in 12 cases (63.1%) andforPCNA in 8 (42.1%). With respect to the bcl-2 labeling index,ono expression of this protein was detected in 12 cases, corresponding to 63.1% of the sample. Based on these findings, it was concluded that p53 and PCNA can favor the proliferative activity of pleomorphic adenomas, whereas bcl-2 probably doesonot effectively particípate in the pathogenesis of this tumor.