VLDL composition has been investigated in two groups of patients: one with Premature Coronary Heart Disease (PCHD) and another one with Insulin Dependent Diabetes Mellitus. Both groups showed abnormal VLDL composition. PCHD patients had VLDL significantly enriched in free cholesterol and triglycerides in comparison with a group of controls matched with patients for sex, age, BMI, serum cholesterol and TG. This VLDL composition indicates a prevalence of big particles, which can be found at the beginning of the lipolytic cascade. On the other hand VLDL of diabetic patients were enriched in cholesterol, especially esterified cholesterol, and apo B in comparison with the respective control group suggesting an increase of smaller VLDL, considered more atherogenic. In conclusion these two studies demonstrate that VLDL compositional abnormalities can be found in two different groups of patients even in the absence of hyperlipidemia.