Fluorescent cytochemical detection of estrogen and progesterone receptors in breast fine-needle aspirates. Estrogen and progesterone receptors were studied in fine-needle aspiration biopsy specimens of 56 patients with primary, recurrent, or metastatic breast carcinoma. The ligands, 17 B-estradiol-6-carboxymethyloxine-bovine serum albumin fluorescein isothiocyanate (FITC-BSA estradiol) and hydroxyprogesterone hemisuccinate bovine serum albumin tetramethyl rhodamine isothiocyanate (TMRITC-BSA progesterone), were used in the fluorescent cytochemical method. The findings obtained from the aspirated cells with the use of the fluorescent cytochemical technique were compared with results obtained from the cell population of the same tumor after removal with the use of both the fluorescent cytochemical technique and the biochemical dextran-coated charcoal (DCC) assay. For the needle aspirates, there was 89% concordance for estrogen receptor and 86% concordance for progesterone receptor between biochemical and cytochemical results. A high degree of correlation was also demonstrated between fine-needle aspirates and imprint preparations with the use of the cytochemical technique. This study suggests that the fluorescent cytochemical technique is an effective tool in assessment of estrogen and progesterone receptor content in fine-needle aspirates of primary and metastatic breast cancer. The fluorescent cytochemical technique can be performed easily at community hospitals and is well suited for specimens of insufficient size for biochemical assay. 