C-erbB-2 (Her-2 or c-neu) expression was studied by immunohistochemistry on FNA specimens of 20 breast ductal carcinomas, 20 fibroadenomas and 20 atypical fibrocystic lesions of the breast. Twelve cases of breast carcinomas, six fibroadenomas and five atypical fibrocystic lesions were found to display c-erbB-2 staining. A significant difference was found among c-erbB-2 index of breast carcinomas (mean 70,25), fibroadenomas (mean 43,83) and atypical fibrocystic disease (mean 37,4). We also found variations in c-erbB-2 expression, among individual cases of breast carcinomas, concerning the number and the intensity of carcinoma cells. It would be interesting to correlate these variations in c-erbB-2 expression with the prognosis of breast carcinomas.