Fine needle aspirates from breast carcinomas of 219 patients were examined cytologically and for the determination of estrogen receptors (ER) and, in 145 of these cases, of progesterone receptors (PR), with the immunocytochemical technique. The traditional biochemical method was also followed for the post-surgical examination of the excised tumour for the determination of the ER and PR contents. In 149 of the 219 cases involving the determination of the ER, and in 112 of those where the PR was determined, the results were compared with those obtained using the biochemical method. Assuming the biochemical technique to be reliable, we obtained the following results with the immunocytochemical method for the ER: 84 true positives, 54 true negatives, 6 false negatives, 5 false positives, 93.3% sensitivity, 91.5% specificity, 94.3% positive predictive value, 90% negative predictive value, 92.6% accuracy, coefficient of correlation 0.83, p = 0.000006. For the PR, we obtained: 42 true positives, 60 true negatives, 6 false positives, 4 false negatives, 91.3% sensitivity, 90.9% specificity, 87.5% positive predictive value, 93.7% negative predictive value, 91.07% accuracy, coefficient of correlation of 0.83, p = 0.000001. Excluding those patients who underwent neoadjuvant treatment, the ER showed 94.3% sensitivity, 98.1% specificity, 98.8% positive predictive value, 91.5% negative predictive value and 95.8% accuracy, and the PR gave 93.3% sensitivity, 93.7% specificity, 91.3% positive predictive value, 95.2 negative predictive value and 93.7% accuracy.