Twenty-one infants were studied to compare cord serum protein concentrations (SPCs) with samples drawn 3 days after birth. The results were compared with anthropometric measurements of the infants to determine the usefulness of serum studies in predicting the nutritional status of the newborn. SPCs of 19 serum protein subfractions were measured by laser nephelometry. In 17 of 19 proteins, the cord blood and newborn blood levels were highly correlated. C1Q and haptoglobin were the exceptions. The SPC was converted to serum protein mass (SPM) as follows: SPM = [(SPC) x (birth weight) x (0.85) x (1-hematocrit)]. Blood volume is approximately 0.85 dl of blood/kg of body weight and since these proteins are largely intravascular, it was postulated that the estimated total protein mass would be a more accurate index of nutritional state. Six proteins (C3, C4, prealbumin, retinol binding protein, transferrin, and albumin) were highly correlated with the anthropometry (arm circumference, skin fold thickness, length, weight, etc.). This study indicates that umbilical cord blood may be used to estimate a newborn's nutritional status. Transport proteins such as albumin, transferrin, retinol binding protein, and prealbumin are commonly used to assess adult nutritional status, and may be used in infants after estimating the total mass of the protein in the serum.