Nucleolar organizer region-associated proteins are argyrophilic and may be visualized by silver stains. This study is a prospective analysis of the AgNOR counts in a range of breast lesions seen in fine needle aspiration (FNA) smears. A total of 72 cases including ductal carcinomas (n = 24), fibrocystic change (n = 24), fibroadenoma (n = 16), proliferative lesions (n = 4) and miscellaneous lesions (n = 4) were studied. The ductal carcinomas showed higher AgNOR counts (mean 16.63 +/- 7.09) compared with the non-malignant lesions (mean 6.39 +/- 1.96), the difference being statistically significant. A cut off AgNOR score of 11 could reliably discriminate malignant from non-malignant lesions. In ductal carcinomas, the AgNOR scores showed a tendency to increase with higher grades of malignancy. There was no correlation with the presence or absence of lymph node metastases at the time of presentation. It is concluded that AgNOR counting, although tedious, is inexpensive, and provides useful information regarding cellular proliferation, and can supplement information obtained by more sophisticated techniques.