Propiverine hydrochloride (P-4) is a new derivative of benzilic acid. The effect of P-4 on the function of the bladder in anesthetized dogs was studied in comparison with flavoxate, which is clinically used for the treatment of pollakiuria. P-4 (4 mg/kg, i.v.) caused a significant increase in maximum vesical volume (Vmax), which was estimated by a cystometrogram. A similar effect was also observed following intravenous administration of verapamil (1 mg/kg), while flavoxate (4 mg/kg, i.v.) caused no significant changes in Vmax. P-4 significantly decreased the frequency of rhythmic bladder contractions at doses higher than 1 mg/kg, i.v., whereas flavoxate first revealed a significant decrease at 4 mg/kg, i.v. Thus the inhibitory effect of P-4 on the micturition movements of the bladder is more potent than that of flavoxate. These findings indicate that P-4 is a useful drug for the treatment of pollakiuria.