The adrenergic αpblocker has been clinically used for the treatment of patients who have micturition difficulty. However, one of its remarkable adverse reactions is orthostatic hypotension, which prevents this kind of drug from being widely used. In the present study a newly synthesized αpblocker, YM-12617, was tried and evaluated in 77 male patients with mild benign prostatic hyperplasia and in 5 women with micturition difficulties of unknown origin. Both 0.2- and 0.4-mg doses relieved the difficulty in about 80% of the patients, subjectively and objectively. A statistically significant decrease in residual urine volume (RUV) and an increase in average flow rate (Qave) and maximum flow rate (Qmax) were observed, especially in the group of patients who received 0.4 mg of this drug, but the maximum urethral closure pressure (UCPmax), maximum bladder capacity (Vmax) and premicturition pressure were unchanged. Neither orthostatic hypotension nor a fall in blood pressure were noted, and adverse reactions were negligible. Hence, the use of this drug seems to be worthwhile for the treatment of patients with mild micturition difficulty.