The relationships between estrogen receptor, progesterone receptor, and a variety of patient characteristics are described for 2,977 women with primary breast cancer. Older women were more likely to be estrogen-receptor positive than younger women. When patient age and menopausal status were analyzed together, age was found to be the primary determinant of increased estrogen-receptor concentrations. There appeared to be no relationship with progesterone receptor for either age or menopausal status when these variables were analyzed separately. But premenopausal women had higher progesterone receptor concentrations than postmenopausal women when patients of the same age were compared, perhaps reflecting greater estrogen-mediated synthesis of progesterone receptor. Tumor size was negatively related to steroid receptor concentrations, but no relationships were observed between steroid receptors and either the number of positive axillary lymph nodes or the location of the primary tumor.