A prospective study was carried out to investigate the effects of the ACE inhibitor captopril on glucose tolerance in 14 elderly patients, aged 76 to 89 years, who had co-incident cardiac failure and stable Type II diabetes mellitus. Patients were maintained on their diet and diabetic therapy and were given 12.5 mg captopril twice daily. Clinical findings, including signs of cardiac failure, body weight and blood pressure, biochemical profile and chest X-ray appearance were documented at each visit. Blood glucose tolerance testing was carried out immediately before starting captopril and again 28 days later. A reduction in symptoms of heart failure occurred in all patients and 5 of them reduced their New York Heart Association grade of heart failure. Significant improvement in glucose tolerance occurred in all patients. Four were able to reduce hypoglycaemic therapy and 1 was able to stop his hypoglycaemic agents. This potentially valuable additional benefit of captopril in improving glucose tolerance has not yet been shown to occur with other ACE inhibitors.