In this multicentre, non-randomized clinical study, 35 hypertensive patients with concomitant non-insulin-dependent diabetes mellitus were treated with the selective alpha 1 adrenoceptor blocker doxazosin mesilate for 24 weeks, either alone or together with existing antihypertensive therapy. The effects of the drug on blood pressure, glucose and lipid metabolism were examined. Daily administration of 0.5-8 mg doxazosin caused a significant reduction in both systolic and diastolic blood pressure decreased from 172 +/- 15/90 +/- 11 mmHg at the beginning, to 149 +/- 19/80 +/- 12 mmHg at the end of the trial. Heart rate was not affected. The plasma glucose level showed no change, whereas the haemoglobin A1c level decreased significantly from 7.4 +/- 1.2% to 7.1 +/- 1.2% (P < 0.01). Total and high-density lipoprotein cholesterol levels remained unchanged. The triglycerides level, however, decreased from 113 +/- 54 mg/dl at the beginning to 98 +/- 49 mg/dl at the end of the trial (P < 0.05). In a subgroup of patients, who showed hypercholesterolaemia ( > or = 220 mg/dl, n = 9) at the beginning, the total cholesterol level decreased from 252 +/- 33 mg/dl to 220 +/- 33 mg/dl (P < 0.05). Two patients complained of abdominal fullness or diarrhoea, but both were easily manageable. The results indicate that doxazosin is effective and safe in the treatment of hypertension in non-insulin-dependent diabetics and does not affect glucose metabolism. As for lipid metabolism in non-insulin-dependent diabetic patients, doxazosin seems to have a beneficial effect.