Ultrastructure of the liver in ventromedial hypothalamus (VMH) lesioned rats was studied in parallel with biochemical examination. Ten weeks after the operation, VMH lesioned rats became markedly obese. Electron microscopic examination of the liver revealed lipid droplets in the cytoplasm and a high load of lipoprotein particles in the Golgi elements. Lipoprotein particles, 40-50 nm in diameter, in the Golgi elements, were scattered throughout the cytoplasm. Concentrations of triglyceride and esterified cholesterol markedly increased in the liver, while those of free cholesterol and phospholipids did not increase. Serum concentrations of triglyceride, total cholesterol and HDL-cholesterol in VMH lesioned rats were higher than control ones. These data suggest that lipoprotein synthesis was markedly increased in the livers of VMH lesioned rats.