Hypertension frequently complicates diabetes mellitus and is associated with an increased incidence of cardiovascular and microvascular complications. Angiotensin-I converting enzyme (ACE) inhibitors are effective antihypertensive agents and it has been suggested that they may improve glucose tolerance. We performed a double-blind, randomized study comparing treatment for 8 weeks with cilazapril, a new ACE inhibitor, or placebo on metabolic variables in 22 hypertensive non-insulin-dependent diabetes mellitus (NIDDM) patients. At week 8 no significant changes in fasting plasma glucose, fasting plasma insulin, haemoglobin A1 and plasma lipids had occurred. The areas under the glucose [placebo (mean +/- SD): 10.7 +/- 3.27 and 10.6 +/- 2.53; cilazapril: 11.9 +/- 3.23 and 12.1 +/- 2.9 mmol/l per 180 min at 0 and 8 weeks, respectively] and insulin curve [placebo (median and range): 47.4 (31.4-165.1) and 65.3 (16.8-190.8); cilazapril: 51.1 (23.8-132.0) and 57.6 (29.0-150.1) mU/l per 180 min at 0 and 8 weeks, respectively] after a standardized oral liquid test meal were unaltered. A significant decrease in mean arterial blood pressure was observed after cilazapril (122 +/- 8.6 and 106 +/- 8.3 mmHg at 0 and 8 weeks, respectively), in contrast to placebo (122 +/- 6.7 and 120 +/- 6.9 mmHg at 0 and 8 weeks, respectively). In conclusion, cilazapril does not affect metabolic control in hypertensive NIDDM patients, whereas it effectively reduces blood pressure.