During puberty, estrogen causes breast maturation and growth of the uterine lining in girls, and accelerates linear growth and bone maturation in both boys and girls. Decreasing the biosynthesis of estrogen can attenuate these processes. In 12 girls with the McCune-Albright syndrome (MAS), in which precocious puberty is due to production of estrogen from ovarian cysts, testolactone (40 mg/kg per day) decreased the volume of ovarian cysts, the frequency of menses, and the rates of growth and bone maturation, for periods of 1-4 years. In a 6-month pilot study of 12 children (eight boys; four girls) with congenital adrenal hyperplasia, testolactone, in combination with an antiandrogen (flutamide), a mineralocorticoid (fludrocortisone acetate, Florinef), and a reduced glucocorticoid dose, improved the control of growth and bone maturation compared with conventional therapy. In a 6-year study of 10 boys with familial male precocious puberty, testolactone, in combination with an antiandrogen (spironolactone), decreased rates of growth and bone maturation, and increased predicted adult height. All patients who developed evidence for gonadotropin-dependent puberty were also treated with a GnRH analog. Testolactone had no important adverse effects in any group of patients, although the need for a four-times-daily dosing schedule made compliance difficult for many families. We conclude that suppressing of estrogen with testolactone was effective therapy, and that more potent and specific inhibitors of aromatase could further improve the treatment of these disorders.