Serum Lipoperoxide levels were studied in 50 normal Korean and in the following patients; 26 patients with diabetes mellitus, 20 patients with hypertension, 14 patients with ischemic heart disease, 8 patients with cerebrovascular accident and 6 patients with nephrotic syndrome. The results obtained are summarized as follows; 1. In normal Korean, the average serum lipoperoxide level was 2.62+/-0.27 nmoles M.D. A./ml, with no difference by the sex. 2. In the cases with various disease which in supposed to be related to abnormal lipid metabolism, that is, diabetes mellitus, hypertension, ischemic heart disease, nephrotic syndrome, the serum lipoperoxide value showed statistically significant elevation compared to that of the normal control (p<0.01), but in the patients with cerebrovascular accident the elevation was not significant (p>0.05). 3. The serum lipoperoxide level was coarsely related with the serum concentration of cholesterol and total lipid, the correlation coefficient of which were 0.34 and 0.35 respectively (p<0.05).