We studied 135 premature newborns of 26 to 36 weeks gestation, divided into three groups: the control group, 66 premature infants with uncomplicated course; 51 premature neonates with appropriate birth weight for gestational age (AGA), who suffered from clinical problems that delayed oral feeding; and 18 premature infants with small birth weight for gestational age (SGA). When neonates of the same postnatal age were compared, prealbumin concentrations were the lowest in the SGA group at the third and fourth postnatal week. Although the AGA group had the most infants with serious illnesses and the lowest protein-calorie intakes, their prealbumin concentrations did not differ significantly from those of the control group. But when the infants of each group were subdivided on the basis of intakes and weight gain regardless of postnatal age, those with greater intakes showed significantly higher prealbumin values; however, in all groups, the infants with higher intakes were also significantly older. Total proteins and albumin showed similar changes in all groups. Prealbumin concentrations showed great interindividual variability in infants of the same postnatal age. We conclude that prealbumin, albumin, and serum total proteins are not sufficiently sensitive biochemical markers to assess alterations of the nutritional status of premature infants.