The fatty acid composition in free fatty acid and phospholipid fraction of plasma in untreated mildly hyperlipidemic patients were determined. The general trend was an increase in saturation in both free and phospholipid fractions of plasma in patients compared with that of healthy controls. Furthermore, arachidonic acid, precursor of formation of prostaglandins and leukotrienes was detected in significantly lower amount in plasma of mildly and untreated hyperlipidemic patients. These fatty acid abnormalities were connected with the increased lipidperoxidation in plasma lipids and in both resting and stimulated granulocytes.