Serum albumin concentrations in infants vary inversely with the degree of maturity, the blood albumin concentration of the premature newborn being lower than that of the baby born at term (I). It is unknown whether this phenomenon reflects reduced albumin synthesis or increased albumin turnover in less mature babies. A diminished synthetic rate appears to explain the hypoalbuminemia observed in malnourished rats (2-6) and children (7,8). However, such nutritional factors probably do not account for the relatively low albumin of babies whose growth is appropriate for gestational age. Immaturity of hepatic mechanisms subserving albumin synthesis might explain the low albumin. Conversely, the catabolism of albumin might be enhanced, especially in light of the observation that total body protein turnover is inversely related to the degree of maturity of premature infants (9).We have measured albumin turnover in a group of premature The results indicate that the relative hypoalbuminemia of premature infants is referable to an enhanced rate of albumin turnover rather than a diminution of albumin synthesis. Indeed, rates of albumin synthesis in these babies are much greater than those reported in the adult, with the albumin half-life in premature babies being less than half the adult value.