We have previously demonstrated alterations in apolipoprotein B-48 metabolism in the post-prandial state in patients with non-insulin-dependent diabetes mellitus. This study investigates the relationship between hypertriglyceridaemia and post-prandial lipoprotein metabolism. Four groups of patients were examined: non-insulin-dependent diabetic patients, with normal serum triglyceride levels (serum triglyceride < 2.1 mmol l-1; haemoglobin HbA1c 5.5% +/- 0.4%); poorly controlled, non-insulin-dependent diabetic patients with hypertriglyceridaemia (serum triglyceride > 2.1 mmol l-1; HbA1c 8.8% +/- 0.9%); non-diabetic subjects with serum triglycerides < 2.1 mmol l-1; and non-diabetic subjects with hypertriglyceridaemia (serum triglyceride > 2.1 mmol l-1). Subjects were studied fasting and following a high-fat meal (1300 kcal). The triglyceride-rich lipoprotein fraction was isolated by ultracentrifugation (d < 1.006 g ml-1). Apoprotein B-48, apoprotein B-100 and apoprotein E were separated on 4%-15% gradient gels and quantified as a percentage of the fasting concentration by densitometric scanning. Triglyceride-rich lipoprotein apolipoprotein B-48 and apolipoprotein B-100 post-prandial profiles demonstrated a maximum increase either at 2 h or rising still further to a peak at 6 h before falling in the diabetic groups and hypertriglyceridaemic non-diabetic subjects when compared with the normotriglyceridaemic control subjects whose levels decreased after 2 h (P < 0.05). A significantly different triglyceride-rich lipoprotein apolipoprotein E profile was also exhibited by the diabetic patients (P < 0.05). Levels of triglyceride-rich lipoprotein, cholesterol, triglyceride, total protein and apoprotein B were elevated in the hypertriglyceridaemic subjects, both diabetic and non-diabetic. These results indicate that hypertriglyceridaemia is associated with altered metabolism and composition of post-prandial triglyceride-rich lipoprotein particles in both poorly controlled diabetic and non-diabetic subjects.