The ABCD (Appropriate Blood Pressure Control in Diabetes) Trial is a large, prospective, randomized clinical trial of 950 patients with non-insulin-dependent diabetes mellitus (NIDDM) designed to compare the effects of intensive blood pressure control with moderate control on the prevention and progression of diabetic nephropathy, retinopathy, cardiovascular disease, and neuropathy in NIDDM. The secondary objective is to determine equivalency of the effects of a calcium channel blocker (nisoldipine) and an angiotensin-converting-enzyme inhibitor (enalapril) as a first-line antihypertensive agent in the prevention and/or progression of these diabetic vascular complications. The study consists of two study populations aged 40-74 years, 470 hypertensive patients (diastolic blood pressure of > or = 90.0 mmHg at time of randomization) and 480 normotensive patients (diastolic blood pressure of 80.0 mmHg at time of randomization). The study duration is 5 years and is scheduled to end in May of 1998. Patients are randomized to receive either intensive antihypertensive drug therapy or moderate antihypertensive drug therapy. Patients are also randomized to nisoldipine or enalapril, with open-label medications added if further blood pressure control is necessary. The primary outcome measure is glomerular filtration rate as assessed by 24-h creatinine clearance. Secondary outcome measures are urinary albumin excretion, left ventricular hypertrophy, retinopathy, and neuropathy. Cardiovascular morbidity and mortality will also be evaluated. Given the data showing the impact of hypertension on complications in NIDDM, the ABCD Trial is designed to determine if intensive antihypertensive therapy will be more efficacious than moderate antihypertensive therapy on the outcome of diabetic complications in NIDDM.