BACKGROUND Type 2 diabetic patients have a higher risk of atherosclerosis than non-diabetic subjects. This difference may be attributable to increased levels of small dense low-density lipoprotein-cholesterol (sLDL-C) in diabetic patients. As the sLDL-C concentration is elevated in hypertriglyceridemia, which is exaggerated postprandially, we examined whether the sLDL-C level increases postprandially in type 2 diabetes. METHODS We obtained 7 blood samples (30min before and 2h after each meal, and at midnight) from 15 patients with diabetes and ten normal controls. Following the precipitation of very low-density lipoprotein and large buoyant LDL (bLDL) with heparin-Mg(2+), the sLDL-C concentration was determined as the cholesterol concentration by a homogeneous assay. RESULTS The fasting sLDL-C concentration was 60.3% higher in the diabetic patients than in the controls (1.01+/-0.21 vs. 0.63+/-0.21mmol/l, p<0.001). The sLDL-C concentrations in both groups were highest in the fasting state, decreased after breakfast, and remained low until midnight. The maximal reduction in the absolute sLDL-C concentration was 56.5% greater in the diabetic patients than in the controls (0.36+/-0.13 vs. 0.23+/-0.16mmol/l, p<0.05). Thus, the sLDL-C/bLDL-cholesterol (bLDL-C) ratio was reduced with increases in bLDL-C. CONCLUSIONS The sLDL-C concentration decreases postprandially in diabetes. This absolute reduction in sLDL-C may contribute to an acceleration of atherosclerosis in diabetic patients.