In a previous series we have shown poor short-term (3-5 years) survival for patients with tumours overexpressing the c-erbB-2 oncoprotein. In this study we employed archival paraffin-embedded tissue from patients who underwent mastectomy 10-12 years prior to assessment (n = 187). Immunohistochemical staining was carried out by an indirect immunoperoxidase technique using the novel monoclonal antibody NCL-CB11. Tumours were scored according to intensity of membrane staining. Patient and tumour information was obtained by scrutiny of clinical records. Survival analysis was carried out for both time to relapse and time to death, using the log rank test. Patients with tumours demonstrating intense membrane staining had a poor prognosis compared with the rest, with a steeply sloped survival curve over the first 4 years; the survival difference was still evident at 12 years follow-up (P less than 0.001). The survival advantage for c-erbB-2 negative patients was maintained in lymph node negative patients (P less than 0.001). However, c-erbB-2 status did not influence survival in the node positive group, where all patients had a uniformly poor outlook. These results applied to both time to relapse and time to death. In conclusion, c-erbB-2 status, determined using NCL-CB11, is a powerful prognostic indicator, defining in particular node negative patients with a particularly poor prognosis, and for whom alternative therapeutic strategies may be appropriate.