The increased activity of hepatic lipase after intraperitoneal insulin administration in IDDM patients appears to be one of the main determinants of lipoprotein changes observed, resulting in the normalization of lipoprotein composition during this mode of therapy. The normal inverse relationship between VLDL triglycerides and HDL cholesterol, which was not present in IDDM patients with subcutaneous therapy, was restored with intraperitoneal insulin regimen.