Abnormal lipoprotein metabolism contributes to the increased risk of premature atherosclerosis in people with insulin-dependent (type I) diabetes. Although hypertriglyceridemia is common in those with untreated IDDM, treatment with conventional insulin therapy usually restores fasting lipoprotein profiles to nondiabetic levels. Intensive insulin therapy improves glycemie control and lipoprotein concentrations, but does not ameliorate the changes in lipoprotein composition described in people with IDDM. Some of these persistent changes in lipoprotein composition have been attributed to peripheral hyperinsulinemia associated with s.c. insulin therapy. The recent availability of implantable insulin-infusion pumps for treatment of IDDM has allowed the study of the effect of i.p. insulin delivery on lipoprotein metabolism, i.p. insulin therapy is capable of maintaining near normal plasma glucose levels while reducing the peripheral hyperinsulinemia. Although results have been contradictory, studies of i.p. insulin therapy may eventually help to determine whether some of the observed changes in lipoprotein metabolism and composition in people with IDDM are due to the peripheral hyperinsulinemia associated with s.c. insulin therapy.