In a prospective study of 50 consecutive fine-needle samples of breast cancer, determination of estrogen and progesterone receptors was performed by separate immunocytochemical and biochemical assays. Comparisons of immunocytochemical assays with biochemical assays were obtained in 42 cases (84%) for both steroid receptors and showed significant relationships for estrogen receptor (P less than 0.001, r = 0.85) and progesterone receptor (P less than 0.001, r = 0.89) when the percentage of labeled nuclei (immunocytochemical assay index) was considered. In addition, DNA flow cytometric analyses were performed on fine-needle samples in 34 cases, with measurable DNA ploidy and S-phase fraction in 33 (97%) and 31 cases (91%), respectively. These results show that (1) estrogen and progesterone receptor immunocytochemical assays are valuable tools for steroid receptor determination, and that (2) on the same fine-needle samples of breast cancer DNA flow cytometric analysis may be performed.