The aim of this study was to characterize abnormalities of triglyceride-rich apolipoprotein (apo) B-containing lipoproteins in type I diabetic patients with elevated albumin excretion rates (AERs). Sixty-four patients (31 men, 33 women) with normoalbuminuria (AER <20 microg/min), 52 (35 men, 17 women) with microalbuminuria (AER 20-200 microg/min), and 37 (17 men, 20 women) with albuminuria (AER >200 microg/min) and 56 healthy control subjects matched for age and body weight were studied. The major finding was increased mass concentrations of the highly atherogenic intermediate-density lipoprotein fraction in patients with microalbuminuria (P < 0.05) and albuminuria (P < 0.05), compared with those with normoalbuminuria. Triglyceride, free cholesterol, cholesterol ester, and phospholipid concentrations in the VLDL, intermediate-density lipoprotein, and LDL (P < 0.05-0.01), as well as total cholesterol, total triglyceride, and apoB concentrations were higher in patients with renal disease than in those without. Notably, there were no differences between patients with microalbuminuria and albuminuria. Only minor compositional changes could be detected. Postheparin plasma lipoprotein lipase (LPL) activities were identical, but hepatic lipase activities were higher in microalbuminuric and albuminuric patients than in normoalbuminuric patients (P < 0.01). LPL activity and VLDL1, (Sf 60-400) (r = -0.528; P < 0.001) and VLDL2 (Sf 20-60) mass concentrations (r = -0.471; P < 0.001) were negatively related. In conclusion, in type I diabetic patients with early renal disease, there are multiple lipoprotein changes, which are potentially atherogenic and may contribute to the excess of macrovascular complications seen in such patients.