Obesity is often complicated by hypertension, and both conditions are risk factors for atherosclerosis. Leptin has attracted attention as a possible cause of hypertension in obese persons. We investigated the effect of a slow-release alpha1-receptor blocker, bunazosin hydrochloride, on leptin levels and insulin resistance in obese hypertensive patients with hyperleptinemia. The subjects were 17 patients (12 men and 5 women aged 56.1 +/- 12.2 years) with essential hypertension who were not receiving alpha1-receptor blockers. They had a body mass index (BMI) > or = 25 kg/m2 and a plasma leptin concentration > or = 5 ng/ml. They received oral therapy with bunazosin hydrochloride at doses of up to 9 mg/day. The plasma leptin concentration, body weight, blood pressure, heart rate, fasting blood glucose, plasma insulin concentration, and free fatty acid level were compared between before and after treatment. Although there was no significant change of BMI, there was a significant decrease of plasma leptin after treatment (10.6 +/- 5.4 ng/ml vs. 8.7 +/- 3.4 ng/ml, p = 0.0128), as well as a significant decrease of plasma insulin (9.8 +/- 4.8 microU/ml vs. 8.1 +/- 4.6 microU/ml, p = 0.0494) and HOMA-R (2.9 +/- 2.1 vs. 2.2 +/- 1.5, p = 0.0237). In conclusion, bunazosin hydrochloride reduced the plasma leptin level and improved insulin resistance in hypertensive patients with obesity and hyperleptinemia.