Cyclophosphamide and other alkylating agents suppress ovarian function in pre-menopausal women. However, endocrine details remain unknown regarding the influence of patients' age and obesity on CMF-induced hormonal changes. We studied changes in endocrine profile due to chemotherapy (CMF) in 70 pre-menopausal patients with axillary node positive, stage II and/or III breast carcinoma. Plasma levels of estrone (E1), estradiol (E2), androstenedione (A2), luteinizing hormone (LH), and prolactin (PRL) were determined on day 1 and 8 of each chemocycle for 12 cycles. After receiving therapy, 23% of the women continued to have regular menstrual cycles (non-amenorrheic group). In the remaining 77%, ovarian function was suppressed, as evidenced by the onset of amenorrhea within 0-11 months (amenorrheic group). The mean time to amenorrhea was 2.83 +/- 0.33 months (SE). The time required to develop amenorrhea inversely correlated to the patient's age. Both incidence of amenorrhea and time to amenorrhea remained unaffected by either patient's obesity or the timing of chemotherapy initiation in relation to menstrual cycle phase (progestational, follicular). Plasma hormone levels fluctuated widely in both groups during the first three chemocycles. During chemocycle months 4 to 10, in the amenorrheic group, plasma E1, E2, and P declined to their baseline levels with a concomitant rise in LH levels. At this time, E1, E2, and P levels were significantly lower in amenorrheics, despite menstrual cycle associated fluctuations in the non-amenorrheic group. Estrogens (E1 and E2) gradually declined further following the onset of amenorrhea in subsequent months. Further data analysis suggests that host age or obesity did not influence CMF-induced changes in the plasma endocrine profile.