Treatment outcome in congenital adrenal hyperplasia is often sub-optimal due to hyperandrogenism, treatment-induced hypercortisolism, or both. We previously reported better control of linear growth, weight gain, and bone maturation in a short term cross-over study of a new four-drug treatment regimen containing an antiandrogen (flutamide), an inhibitor of androgen to estrogen conversion (testolactone), reduced hydrocortisone dose, and fludrocortisone, compared to the effects of a control regimen of hydrocortisone and fludrocortisone. Twenty-eight children have completed 2 yr of follow-up in a subsequent long term randomized parallel study comparing these two treatment regimens. During 2 yr of therapy, compared to children receiving hydrocortisone, and fludrocortisone treatment, children receiving flutamide, testolactone, reduced hydrocortisone dose (average of 8.7 +/- 0.6 mg/m2 x day), and fludrocortisone had significantly (P < or = 0.05) higher plasma 17-hydroxyprogesterone, androstenedione, dehydroepiandrosterone, dehydroepiandrosterone sulfate, and testosterone levels. Despite elevated androgen levels, children receiving the new treatment regimen had normal linear growth rate (at 2 yr, 0.1 +/- 0.5 SD units), and bone maturation (at 2 yr, 0.7 +/- 0.3 yr bone age/yr chronological age). No significant adverse effects were observed after 2 yr. We conclude that the regimen of flutamide, testolactone, reduced hydrocortisone dose, and fludrocortisone provides effective control of congenital adrenal hyperplasia with reduced risk of glucocorticoid excess. A long term study of this new regimen is ongoing.