Urinary and blood hormonal profiles were studied throughout a monthly cycle in a patient with familial breast cancer. Two comparison cohorts (one high-risk and one low-risk) were studied concurrently. Findings disclosed that our breast cancer-affected patient showed a distinctive hormonal pattern characterized by significant elevation throughout the cycle of plasma estrone, estradiol, and prolactin. Save for a depression in plasma FSH in the early follicular phase, this hormone, as wells as LH and progesterone patterns in our patient, were similar to the comparison cohorts. Urinary estrone and estradiol patterns in our patient were elevated early in the follicular phase. Our patient also showed a depression in urinary estrone, estradiol, and estriol following ovulation, which persisted throughout the luteal phase. Blood and urinary hormone patterns in the high-risk cohort were not demonstrably different from the low-risk cohort, with the exception of plasma prolactin. The results on the latter hormone showed an unexpected significant depression throughout most of the menstrual cycle in this low-risk cohort. We conclude that estrone and estradiol elevations, as clearly evidenced in our breast-cancer-affected patient, may provide clues that ultimately might be used as an etiologic discriminant for breast cancer risk and which may also play a pathogenic role in this disease. Since this involved a single patient, our conclusions must be interpreted cautiously.