Terazosin, a selective, long-acting alpha 1-adrenergic blocker, was evaluated in 44 men with benign prostatic hyperplasia. The dose was titrated from 2 to 20 mg nightly depending on improvement in symptoms and flow rate. All men completed at least 3 months of therapy, 26 had 6 months and 19 received 9-12 months of terazosin. There was an average increase of 2 ml/s in the peak urinary flow rate compared to baseline. This was statistically significant at the 3-month level. Residual urine decreased under treatment at each 3-month time interval. Prior to initiation of terazosin the mean was 165 ml, and it was 62, 100, and 41 ml at 3, 6 and 9 months respectively. There was a statistically significant improvement in both the obstructive and irritative symptom scores. Side effects were minimal; only 1 patient discontinued terazosin due to a hypotensive episode. Terazosin was found to be safe and effective in the dose range of 2-20 mg taken at bedtime in men with symptoms related to benign prostatic hyperplasia. The present study did not identify any baseline parameters such as initial prostate volume, peak flow rates, or obstructive or irritative symptom scores that correlated with clinical outcome.