As already reported in Part I, lipid metaboism in platelets was abnormal in hyperlipidemic, arteriosclerotic patients and diabetics. In order to investigate this abnormality, several experiments were performed on hyperlipidemia induced by lanolin and cottonoil in rabbits and on the effects of some drugs and food intake on lipid metabolism in human platelets. The results are summarized as follows. 1. The (14)C incorporation into total fatty acid of platelets from hyperlipidemic rabbits was increased and the abnormal pattern of the (14)C incorporation into fatty acid was the same as in hyperlipidemic patients and the (14)C incorporation into oleic acid was markedly increased. 2. With addition of 100γ/ml of BAL or 100γ/ml of Antimycin A, an abnormal pattern of (14)C incorporation into fatty acid was observed. This was similar to that observed in hyperlipidemic patients and (14)C incorporation into oleic acid was increased absolutely. 3. When ATP or Insulin was added, the (14)C incorporation into total fatty acid was increased. 4. It was disclosed that platelets obtained after meal incorporated more (14)C-acetate into total fatty acid than those before meal and this incorporation was more prominent in hyperlipidemic patients.