A multicenter, randomized, double-blind study was undertaken to evaluate the efficacy of the antiandrogen flutamide in treating patients with urinary obstruction caused by benign prostatic hypertrophy (BPH). Patients were randomized to either flutamide (750 mg/d) or a placebo. Prostate size (measured by ultrasound), uroflow, and symptomatology were assessed in all patients. Of the 84 patients entered in the study, 30 receiving placebo have, to date, reached twelve weeks and 4 have reached twenty-four weeks. Twenty-eight patients receiving flutamide have reached twelve weeks, while 8 have reached twenty-four weeks. At twenty-four weeks, a 41 percent median decrease in prostate volume and a 46 percent increase in full-bladder uroflow was observed in patients receiving flutamide; no significant changes in prostate volume or uroflow occurred in patients receiving placebo. However, significant symptomatic improvements were noted in both groups. Only 4 patients (11%) had significant adverse reactions to flutamide; these reactions included breast pain and diarrhea. No cases of impotence occurred. It was concluded that flutamide may be a safe and effective drug for the treatment of symptomatic BPH.