The very low density lipoprotein (VLDL) fraction was isolated from 11 normolipidaemic Type 1 (insulin-dependent) diabetic patients in good to fair glycaemic control and from 11 age-, sex- and race-matched, non-diabetic, control subjects. The rate of receptor-mediated degradation by human endothelial cells was significantly greater (p < 0.02) for the total VLDL fraction isolated from diabetic patients compared to control subjects and averaged 1008 +/- 300 and 717 +/- 150 ng.mg cell protein-1.16 h-1, respectively. The total VLDL fraction was separated into three subfractions: VLDL-I, Sf 100-400 (Sf = Svedberg units); VLDL-II, Sf 60-100; VLDL-III, Sf 20-60. Rates of receptor-mediated degradation of VLDL-I and VLDL-II isolated from diabetic patients were significantly greater than the comparable subfraction isolated from control subjects and averaged 1023 +/- 279 vs 361 +/- 122 (p < 0.01) and 433 +/- 70 vs 294 +/- 70 ng.mg cell protein-1.16 h-1 (p < 0.03), respectively. Rates of receptor-mediated degradation of the V-III subfraction isolated from the two groups did not differ significantly. There were no significant differences in the chemical composition or in the plasma concentrations of the VLDL subfractions isolated from diabetic patients compared to control subjects. There was a significant increase in the apoprotein E content of VLDL-I (p < 0.01) and VLDL-II (p < 0.05) isolated from diabetic patients. There was a significant increase in the ratio of apoprotein C compared to apoprotein E (p < 0.03) in VLDL-I isolated from control subjects compared to the diabetic patients.(ABSTRACT TRUNCATED AT 250 WORDS)