Estrogen receptors (ERs) and progesterone receptors (PRs) were determined by an immunocytochemical assay (ICA) on fine needle aspirates (FNAs) from patients with primary, recurrent and metastatic mammary carcinoma, and the results were compared to those with the biochemical dextran-coated charcoal (DCC) method performed on the surgical sample in order to compare the two methods. The aspirates were suspended in a buffered saline solution, cytocentrifuged onto glass slides and immunocytochemically stained according to the protocol of commercial kits employing monoclonal antibodies specific for ER and PR. Immunocytochemical staining of malignant cells was evaluated on the basis of the percentage of stained cells; 10% staining was taken as the cutoff value. Fine needle aspiration biopsies (FNABs) from 107 breast carcinomas were analyzed immunocytochemically for ER and 31 of them for PR, also. The overall concordance between ICA and DCC was 88% for ER and 87% for PR. The sensitivity, specificity, and positive and negative predictive value of ICA on FNAs as compared to conventional DCC were 87%, 90, 97% and 63%, respectively, for ER and 85%, 100%, 100% and 56% for PR. These findings suggest that estrogen immunocytochemical assays and progesterone immunocytochemical assays on FNAs in breast cancer patients are reliable techniques for evaluating receptor status and can be useful in assessing ER and PR whenever surgical biopsy is not indicated and when information about ER and PR status is required at the time of the clinical diagnosis.