The assessment of nucleolar organising regions have been reported to be of prognostic value both in a number of haematological and solid tumours. We have examined the relationship between the number of nucleolar organising regions (NORs) present in 75 primary breast cancers and various clinical and pathological features known to be associated with prognosis in patients with breast cancer. Formalin-fixed, paraffin-embedded tumour tissue was sectioned and stained by a one-stage argyrophil (AgNOR) method. Using light microscopy the mean number of AgNORs per cell was calculated. No correlation was observed between AgNOR counts and any of the prognostic variables studied, including oestrogen receptor (ER) status, histological grade of malignancy, lymph node stage or site of initial metastatic disease. Similarly there was no correlation between AgNOR counts and disease-free interval or survival. AgNOR counts do not appear to be a prognostic factor in primary breast cancer.