A study has been made on the lipid composition of the skin secretions and plasma of the neonatal calf. A significant proportion of the skin surface lipids was comprised of triglycerides. Saturated fatty acids comprised the major proportion of the fatty acids of the skin surface triglycerides at birth. Immediately after birth, the proportion of the saturated fatty acids decreased, and there was a concomittant increase in the proportion of 18:1. Some 3-4 weeks after birth, the proportion of 18:2 delta cis-9, cis-12 in the skin surface triglycerides increased to ca. 14 percent, and there was a decrease in the proportion of 18:1. The 18:2 was shown to be confined almost entirely to the 2 position of the triglycerides. During the first 5 weeks after birth, the concentrations of the cholesteryl esters and phospholipids in the plasma increased markedly and were accompanied by a rapid increase in the proportion of 18:2 within these 2 fractions. The results are discussed in relation to the known role of 18:2 in the metabolism of biological systems.