To document whether c-erbB-2 over-expression or p53 accumulation in tumour cells was predictive of response to chemo- or radiotherapy, we analyzed a population of patients with breast cancer assigned to neo-adjuvant therapy (median follow-up: 54 months). T2/T3-N0N1b-M0 tumours (329 cases) were treated either by FAC chemotherapy or by radiotherapy before surgery, and the clinical response was classified as complete or incomplete. Expression of c-erbB-2 and p53 was retrospectively evaluated by immunohistochemistry. Proliferation rate was assessed by means of MIB-1 antibody and by S-phase fraction. A complete response to chemotherapy was observed in 38/167 patients (23%). Complete response rate was 20% in c-erbB-2-negative tumours, and rose to 31% in tumours with c-erbB-2 over-expression, but this trend was not statistically significant. There was no correlation between p53 staining and response to treatment, whereas chemosensitivity was found correlated with histological grade and S-phase. A complete response to radiotherapy was observed in 64 of the 156 evaluable patients (41%). Complete response rate was 41% in c-erbB-2- or p53-negative tumours, 54% in tumours with c-erb-B-2 over-expression, and 44% in tumours with p53 accumulation. There was no correlation between response to radiotherapy and histological grade or proliferative rate. No prognostic value was found for c-erbB-2 or p53 expression, whereas the 5-year survival rate was 85% for patients presenting a tumour with a low proliferating index (MIB-1 < 10%), and 68% for patients presenting a tumour with a high proliferative index. In multivariate analysis, node status (RR = 2), MIB-1 immunostaining (RR = 2), and tumour size (RR = 1.8) were found to be associated with survival. These results indicate that c-erbB-2 or p53 expression is not significantly associated with tumour response to neo-adjuvant chemo/radiotherapy in our series of breast cancers.