Seventy-six effort angina patients who had typical angina on exertion documented by treadmill stress test with evidence of ischemic ST-segment depression and 78 healthy volunteers in urban Japan were investigated in this study. Plasma free fatty acids (FFA) in both groups were determined using high-performance liquid chromatography. The relationships between the total cholesterol, high-density lipoprotein (HDL), triglycerides in plasma, and the genesis of coronary heart disease were also examined. The ratio (0.08 +/- 0.08) of eicosapentaenoic acid (EPA)/arachidonic acid (AA) in plasma FFA was significantly lower in effort angina patients than that (0.15 +/- 0.12) in healthy volunteers. The lower ratio was due to significantly lower levels of EPA in the patients than in normals. In 42% of angina patients, the ratio is below 0.03. In all age subgroups except the age 30-39 subgroup, the ratio of EPA/AA was significantly lower in patients than in normals, when divided into four subgroups by using a 10-year age interval. Though the total cholesterol and triglycerides were not significantly different between the two groups, HDL was significantly lower and total cholesterol/HDL ratio was significantly higher in effort angina patients than in healthy volunteers. However, there was no correlation between EPA/AA ratio and HDL in individuals in either group. From these results, it could be concluded that lower EPA/AA ratio is a new coronary risk indicator other than HDL.