Silver staining nucleolar organiser regions (AgNOR's) were determined in archival histological specimens of breast carcinoma. Representative samples from forty-eight female patients were counted manually for AgNOR's--median 3.85 (range 1.1-10.2 AgNOR's per cell). Taking the median value of 3.85 as a cutoff, the patients were divided into two groups: A = Those with AgNOR counts > 3.85; B = Patients with AgNOR counts < or = 3.85. The 5 year survival was 21% in group A and 85% in group B (p < 0.001). There was no significant correlation between AgNOR's and tumour size, lymph node status, tumour grade, menopausal status and oestrogen receptors. We conclude that nucleolar organiser regions may be useful as a prognostic indicator in breast carcinoma especially in patients in whom other prognostic information is unavailable.