The pharmacokinetics and pharmacodynamics of the a1-blocker bunazosin were studied in 9 patients with renal insufficiency and 11 healthy control subjects after a single oral administration of 3 mg. Plasma and urinary drug concentrations were determined using high-pressure liquid chroma-tography. The pharmacokinetic parameters of bunazosin elimination half-life and time to peak level were not statistically significantly affected by renal insufficiency. Peak level and area under the plasma concentration-time curve were significantly increased in patients with renal insufficiency compared with control subjects. In addition, plasma clearance and the apparent volume of distribution were significantly smaller in patients with renal insufficiency than in normal subjects. The urinary excretion of bunazosin was not affected by renal insufficiency. Although the normal subject group was not age matched with the patient group, it has been reported that the pharmacokinetics of bunazosin are not affected by age. These results suggest that hepatic metabolism is decreased in renal insufficiency. Concerning the pharmacodynamic effects, the changes in diastolic blood pressure and heart rate were weak but statistically significantly related to plasma bunazosin concentrations. There was no correlation between systolic blood pressure and plasma bunazosin levels. Hysteresis was observed between plasma drug levels and the pharmacodynamic effects.