Both preoperative cytological (FNS) and tumorectomy surgical specimens of the same tumor were obtained from 89 patients with breast cancer. Estrogen and progesterone receptors were assayed on cytosolic extracts by enzyme immunoassay (EIA), in 89 patients for estrogen and in 68 patients for progesterone. Both concentrations were highly correlated between the FNS and the corresponding surgical sample, but FNS values yielded 2 to 3 times higher. With cut-off values of 250 fmol/mg DNA, corresponding to 15 fmol/mg cytosol protein for surgical samples and 500 fmol/mg DNA for FNS, the receptor status was concordant between the types of samples in 84 of 89 (94%) and 59 of 68 (86.8%) patients for estrogen and progesterone, respectively. Sixty-seven carcinomas were estrogen positive, 17 estrogen negative, 38 progesterone positive, and 21 were progesterone negative in both samples. The authors conclude that estrogen and progesterone EIAs can be performed on FNS provided by properly trained pathologists, with a control of their cellularity by DNA assay.