Studies have demonstrated that "antihypertensive" treatment with angiotensin-converting enzyme inhibitors (ACEI) may retard the progress of nephropathy in patients with insulin-dependent diabetes mellitus. To obtain an indication of the potential effect of ACEI treatment and as a guide to future research, the effects of screening and early ACEI treatment programs were estimated using cost-effectiveness models. The preliminary analysis suggests that the early treatment of insulin-dependent diabetes mellitus patients with ACEI is likely to be a very cost-effective use of health care resources. The cost-effectiveness ratio for screening and treatment at the stage of microalbuminuria ($7,900 to $16,500 per year of life saved) compares favorably with those of other medical life-saving interventions. Less-aggressive programs (screening followed by treatment at the stage of proteinuria) would improve life expectancy to a lesser extent but could save net health care costs as well as years of life. Although more exact and comprehensive cost-effectiveness analysis must await clinical trials, these illustrative results demonstrate the range of cost-effectiveness that can be expected from these programs and identify data needed for more decisive policy conclusions.