A group of consecutive 180 veteran patients with mild to moderate essential hypertension were chosen to participate in clinical antihypertensive trial for the purpose of defining the role of converting enzyme inhibitors and renin-angiotensin-aldosterone system in the management of mild to moderate hypertension patients. After a two-week placebo period, these patients were randomly assigned to regimens of converting enzyme inhibitors (enalapril or captopril with or without diuretics) or conventional therapy (diuretics with or without traditional vasodilators with or without beta-blockers). Each patient was regularly followed up every two weeks and doses were added until the diastolic blood pressure was equal to or lower than 90 mmHg. After 1 year of follow-up, only 162 patients completed the study. All high blood pressure was significantly reduced by these three regimens, but no significant difference of blood pressure control was noted. The mean left ventricular ejection fraction increased from 55.9 +/- 6.2 to 57.5 +/- 5.3% in captopril group (P less than 0.05, n = 59) and from 54.8 +/- 6.8 to 57.2 +/- 5.8% enalapril group (P less than 0.01, n = 53), in contrast to the insignificant change in control group (n = 50) (56.5 +/- 7.7 to 56.6 +/- 5.9%). The exercise duration also significantly increased only in converting enzyme inhibitors group (P less than 0.01). Furthermore, the plasma aldosterone level was significantly reduced by converting enzyme inhibitors therapy, whereas conventional therapy had no beneficial effect (P less than 0.01). Furthermore, the plasma aldosterone level was significantly reduced by converting enzyme inhibitors therapy, whereas conventional therapy had no beneficial effect (P less than 0.001). Concomitantly, antidiuretic hormone and plasma norepinephrine levels were also significantly reduced by converting enzyme inhibitors. In addition, converting enzyme inhibitors had a favorable trend to affect the metabolism of lipid in contrast to the conventional therapy. These results show that a first-step treatment of hypertension with converting enzyme inhibitors permits better left ventricular function and improves exercise tolerance by way of renin-angiotensin-aldosterone system inhibition. Thus, converting enzyme inhibitors might be suggested as the first step regimen in the treatment of hypertension.