From 1950 to 1980, the gross alteration in dietary habit in Japan was noted. Intake of total calories has markedly increased. This could be most likely due to a remarkable increase in intake of fat, especially animal fat, egg and milk products. A marked decrease of mortality rate due to cerebral hemorrhage and in contrast a marked increase of mortality rate due to cerebral infarction and ischemic heart disease were noted. An epidemiological study of the intake of fish meat (EPA intake) and the mortality rate of adult diseases was performed in a fishing area and in a farming area in Chiba Prefecture. Intake of fish meat (EPA) by the residents of the fishing area was 2-3 times higher than by the residents of the farming area. The mortality rate due to ischemic heart disease and cerebral vascular diseases tended to be lower in the fishing area than in the farming area. EPA manufactured from sardine oil was orally given to normal subjects and to patients with cerebro- and cardiovascular diseases for 4-16 weeks. Significantly decreased platelet aggregation, decreased platelet retention, lowered whole blood viscosity, prolonged bleeding time, increased erythrocyte deformability, improvement of hyperlipidemia, and clinical improvement in some patients were noted. 12-Lipoxygenase metabolites of EPA (12-HPEPE) and arachidonic acid (12-HPETE) have an equipotent inhibitory action on platelet function.