Summary— In order to document further the onset of action of alfuzosin, a selective alpha-1 blocker, 93 symptomatic patients with benign prostatic hypertrophy were randomly allocated to a single oral dose of either alfuzosin 1.25 mg or 2.5 mg, or placebo, after a 1-week placebo lead-in period. The effects on flow rates were assessed 1 h 30 min after administration. Peak and mean flow rates were significantly increased in the alfuzosin groups, as compared with placebo, in a dose-dependent manner. After a single intake of placebo, the mean values of these 2 parameters showed little change. The effect on the cardiovascular system (heart rate and blood pressure) was mild. This study indicates that the action of alfuzosin is already present 1 h 30 min after administration.