The effect of doxazosin, an alpha 1-adrenoceptor blocking drug, on blood pressure, sensitivity to insulin and serum lipids has been evaluated in 14 hypertensive, non-insulin dependent diabetic patients. The dose was titrated individually upwards from 1 mg until the diastolic blood pressure was below 90 mm Hg, side-effects precluded further dosage increase or the maximum daily dose of 16 mg was achieved. After 12 weeks of treatment (mean doxazosin dose 5.6 +/- 5.1 mg daily), the supine and standing diastolic blood pressure of the patients had declined by about 7 mm Hg, whereas their systolic blood pressure and heart rate were not significantly changed. The metabolic clearance rate of glucose increased from 2.35 to 3.37 ml.min-1.kg-1 during treatment, suggesting improved sensitivity to insulin. Fasting plasma glucose was 11.9 mmol.l-1 before and 10.9 mmol.l-1 after doxazosin therapy (NS). Serum electrolytes and lipids did not change significantly but serum uric acid decreased from 305 to 281 mumol.l-1. Doxazosin may be a useful alternative for the treatment of hypertension in NIDDM patients.