Programmed cell death is an important determinant of the response to chemotherapy. Among the factors controlling this process, a significant role is played by bcl-2 and p53, the expression of which, together with estrogen receptor content and tumor proliferative activity, was investigated by means of immunohistochemistry in 55 advanced breast cancer patients (median age, 60 years; range, 25-71 years). Analysis of bcl-2 expression identified two groups of patients with a significant difference in response rate. A total of 17 patients (31%) responded to chemotherapy (5 had a complete response and 12 had a partial response): 14 of 32 (44%) bcl-2-negative patients (< 40% stained cells) and only 3 of 23 (13%) bcl-2-positive patients (> or = 40% of stained cells; P = 0.019 by Fisher's exact test). The two groups were well balanced in terms of age, performance status, disease-free survival, menopausal status, and type of chemotherapy. bcl-2-negative tumors showed a tendency toward a higher p53 expression and proliferation rate, whereas an excess of bone as the dominant disease site was evident among the bcl-2-positive ones. However, the only variable to result significantly different between the two groups was estrogen receptor expression (P = 0.004). A multivariate logistic regression model showed that bcl-2 maintained its power of discriminating two groups with a different probability of responding to chemotherapy, although the greatest contribution was given by dominant disease site and type of chemotherapy. In conclusion, the results of this study suggest a possible role for bcl-2 in predicting resistance to chemotherapy.