OBJECTIVE This study was designed to examine the immunohistochemical expression of bcl-2, p53, and proliferating cell nuclear antigen (PCNA) and the relation of this expression to clinicopathological characteristics and prognosis in renal cell carcinoma (RCC). METHODS The expression of bcl-2, p53 protein, and PCNA was studied by immunohistochemical methods in paraffin-embedded nephrectomy specimens from 53 patients whose clinicopathological data had already become clear. RESULTS The expression of the bcl-2 protein was recognized in 34 cases (64%); the expression of the p53 protein, however, was seen in only 1 case. Bcl-2 positivity was not associated with any pathological parameters or prognosis. If the percentage of PCNA-positive cancer cells as compared to the total amount of cancer cells was defined as a labeling index (LI), a high PCNA LI number correlated significantly with a high T category, high grade, venous invasion, and shortened survival. Among the conventional pathological parameters, the T category, nuclear grade, and venous invasion had the most significant effect on prognosis. A multivariate analysis in the parameters of PCNA, T category, nuclear grade, and venous invasion demonstrated that only nuclear grade had a significant effect on prognosis. CONCLUSIONS The inhibitory effect of the bcl-2 gene on apoptosis related to tumor development is not clear, and the expression of the p53 protein is uncommon in RCC. PCNA seems to be a good objective and quantitative marker of the biological malignant potential in RCC, although the assessment of malignant potential in combination with conventional pathological parameters is indispensable.