Due to the metabolic changes induced, e.g. in the liver by anti-epileptic drugs, the significance of high serum triglyceride and cholesterol in epileptics was studied and the plasma HDL cholesterol level was compared in 190 epileptic patients with elevated or normal triglyceride and cholesterol, with the corresponding values in 43 healthy subjects. One-third of the epileptic patients showed elevated plasma HDL cholesterol levels. Female epileptics had higher plasma HDL cholesterol than the normolipidemic healthy subjects. Epileptics with elevated triglyceride or a combination of elevated triglyceride and cholesterol had a lower plasma HDL cholesterol level than normolipidemic patients with epilepsy. HDL cholesterol level in epileptics with high serum cholesterol did not diverge from the level in epileptics with normal serum triglyceride and cholesterol. The results show significant differences of plasma HDL cholesterol between epileptic patients and normolipidemic healthy controls on one hand, and between epileptics with altered and epileptics with normal serum lipid levels on the other. The findings suggest that the increase of plasma HDL cholesterol level in epileptics undergoing anticonvulsant treatment is influenced by endogenous triglyceride metabolism.