Thirteen hypetensive non-insulin dependent diabetics (9 male, 4 female, mean age 61.6 +/- 6 years) were given 6 weeks treatment with captopril in a dose range 75-150 mg/day. Each patient underwent a standard glucose tolerance test and had blood pressure profiles recorded before and after captopril. Supine systolic blood pressure (mmHg) improved from 181 (+/- 16) to 162 (+/- 17) and diastolic blood pressure from 103 (+/- 11) to 89 (+/- 9). A similar improvement was seen in erect systolic (174 +/- 19 to 156 +/- 19) and diastolic (103 +/- 14 to 87 +/- 11) blood pressures. Following treatment there was no significant change in glucose tolerance although the 120 minute plasma glucose value improved from 15.3 +/- 4.2 to 13.9 +/- 3.4 mmol/l (P less than 0.05). The drug was well tolerated and free of adverse effects. Captopril would therefore appear to be an effective and safe anti-hypertensive agent in non-insulin dependent diabetes and did not result in any deterioration of glucose tolerance.