Two balance studies were performed on each of five infants of low birth weight. About 230 ml/kg/day of S.M.A. S26 milk was given during one study and 180 ml/kg/day during the other. The proportion of nitrogen, fat, and calories retained was similar in the two studies, suggesting that the larger weight gains on the high-volume feeds were due to growth rather than retention of water or excessive deposition of fat.