BACKGROUND: Men with benign prostatic hyperplasia can be treated with alpha 1-adrenergic-antagonist drugs that relax prostatic smooth muscle or with drugs that inhibit 5 alpha-reductase and therefore reduce tissue androgen concentrations. However, the effects of the two types of drugs have not been compared. METHODS: We compared the safety and efficacy of placebo, terazosin (10 mg daily), finasteride (5 mg daily), and the combination of both drugs in 1229 men with benign prostatic hyperplasia. American Urological Association symptom scores and peak urinary-flow rates were determined at base line and periodically for one year. RESULTS: The mean changes from base line in the symptom scores in the placebo, finasteride, terazosin, and combination-therapy groups at one year were decreases of 2.6, 3.2, 6.1, and 6.2 points, respectively (P<0.001 for the comparisons of both terazosin and combination therapy with finasteride and with placebo). The mean changes at one year in the peak urinary-flow rates were increases of 1.4, 1.6, 2.7, and 3.2 ml per second, respectively (P<0.001 for the comparisons of both terazosin and combination therapy with finasteride and with placebo). Finasteride had no more effect on either measure than placebo. In the placebo group, 1.6 percent of the men discontinued the study because of adverse effects, as did 4.8 to 7.8 percent of the men in the other three groups. CONCLUSIONS: In men with benign prostatic hyperplasia, terazosin was effective therapy, whereas finasteride was not, and the combination of terazosin and finasteride was no more effective than terazosin alone.