Male Japanese white rabbits were injected subcutaneously with methyl iodide (57 mg/kg body weight/day) on two successive days and their lipid metabolism was investigated 48 hr after the last injection. The plasma triglyceride levels increased from the preinjection average of 56.1 mg/dl to 246.0 mg/dl on an average, the individual values being greatly variable. Analysis of lipoprotein profile of plasma showed a significant increase of very low density lipoproteins (VLDL). Lipolytic activities in postheparin plasma did not change. However, rates of triglyceride secretion into plasma, measured by Triton WR 1339 injection method, were significantly higher in the animals treated with methyl iodide than in the controls. Histological investigation of the liver showed diffuse fat deposits in the hepatocytes without any destructive and inflammatory changes. The results indicate that hyperlipidemia and fatty liver of rabbits induced by methyl iodide is related to the elevation of triglyceride synthesis and its secretion in the liver.