Because prostatic surgery is not the treatment of choice for most patients with benign prostatic hyperplasia (BPH), the therapeutic effect of a 160-mg, twice-daily, oral dose of Serenoa repens extract was studied during a 3-month open trial in 505 patients with mild-to-moderate symptoms of BPH. The efficacy of the regimen was evaluated in 305 of these patients. Traditional parameters for quantifying prostatism, such as the International Prostate Symptom Score, the quality of life score, urinary flow rates, residual urinary volume, and prostate size, were found to be significantly improved after only 45 days of treatment. After 90 days of treatment, a majority of patients (88%) and treating physicians (88%) considered the therapy effective. In addition, the serum prostate-specific antigen concentration was not modified by the drug, thus limiting the risk of masking any possible development of prostate cancer during treatment. The incidence of side effects (5%) was low and compares favorably with that reported for existing medical therapies used in BPH patients. The extract of Serenoa repens appears to be an effective and well-tolerated pharmacologic agent in treating the mictional problems accompanying BPH.