Animals intoxicated by lead present alterations in the fatty acid composition of red blood cells (RBC). Since this altered fatty acid com position of membranes may be a general reflection of lead toxicosis, we have examined 12 clinically healthy leadexposed male subjects for fatty acid composition of RBC membranes along with blood lead, serum calcium, and serum iron concentrations. Twelve unexposed age-matched male subjects were used as controls. Significantly increased levels of arachidonic acid (AA) were found as compared to matching healthy controls in the RBC of the leadexposed subjects. The increase of AA correlated in a dose-dependent manner with elevation in lead, and with serum iron, while a negative correlation was found between AA and serum calcium. The known ability of lead to substitute for calcium, which is essential in activating phospholipase A2for AA release from membrane phospholipids, may be the main reason for increased AA in RBC membranes.