Twelve type I diabetic patients with established diabetic nephropathy were treated for 12 months with the insulin pump to determine whether glucoregulation would influence the clinical course of proteinuria. All of the subjects were known to have arterial hypertension and were receiving antihypertension medication. Despite good glucose control, as assessed by total glycosylated hemoglobin level, two clinical courses were observed: six patients demonstrated a progression in proteinuria and six appeared to experience a reduction in proteinuria. The group demonstrating a progression had significantly higher mean arterial pressure at six and 12 months of study compared with the group with a reduction in proteinuria. These results suggest that arterial hypertension is an important risk factor in the progression of diabetes nephropathy. Further studies should be designed to recognize early proteinuria and hypertension to determine whether mean normal glucose values and BP over a prolonged period will prevent renal failure.