Ovarian failure is often brought about by the conditioning protocol used for bone marrow transplantation (BMT). We monitored ovarian function in 31 girls conditioned for BMT at 10.3 +/- 0.6 (s.e., 3.2-17.5) years by chemotherapy alone (group 1, n = 8) or chemotherapy plus body irradiation (12 Gy, fractionated in group 2, n = 9, or 10 Gy single total body in group 3, n = 7, and 5 or 6 Gy single thoraco-abdominal in group 4, n = 7, irradiation) at 13.4 +/- 0.4 (11.7-18.6) years. Breast development was normal (n = 11), did not occur (n = 14), or did not progress spontaneously (n = 2) after BMT. The other four girls who menstruated before BMT had permanent amenorrhea. Basal plasma gonadotropin concentrations were measured in 29; follicle-stimulating hormone was increased in them all and luteinizing hormone in 23. At the last clinical evaluation at 16.3 +/- 0.4 (12.1-21.6) years, 23 girls had complete ovarian failure, two had partial ovarian failure, and six had normal ovarian function. Three of these were the youngest group 1 patients and those who had not received busulfan. We conclude that conditioning for BMT given during childhood frequently prevents normal estrogen secretion at puberty. Adequate substitutive treatment may be necessary to induce growth acceleration and sexual development.