The bcl-2 gene encodes a protein which inhibits programmed cell death (apoptosis). This protein was detected by immunohistochemical techniques in 48% of invasive ductal carcinomas of the breast. It was present in well-differentiated carcinomas with hormonal receptors, and proteins synthesized under the control of oestrogens: pS2, cathepsin D and ERD5. In contrast, bcl-2+ carcinomas are less frequently positive for p53 and have a Ki67 score under the mean. bcl-2 protects cells against apoptosis. Accumulation of p53 protein, which is indicative of p53 mutation, would have the same effect; however, these two proteins seem inversely related, an inverse correlation observed by others in breast cancer cell lines and in lymphomas. Tumours positive for bcl-2 escape apoptosis and have worse prognosis but this is not what is found; survival at 5 years, and particularly the absence of recurrence during the first 5 years after surgery, seem to be associated with bcl-2 positivity. The bcl-2 protein seems only to be an important prognostic factor in women over 54 years of age. Moreover, p53-bcl-2+ tumours have a better response to hormonal therapy than p53-bcl-2-tumours.