Compared with other racial groups, African-American women show a disproportionately high risk of delivering low birthweight babies. In a retrospective study of African-American infants born at Meharry Hubbard Hospital, which predominantly serves the underprivileged inner-city poor, free amino acid concentrations were measured in umbilical venous serum from infants born following 34 to 42 weeks gestation. Significant reductions in levels of glycine, serine, alanine, the branched-chain amino acids, and the sum of the so-called dispensable amino acids were associated with decreased birthweight. Glycine, a quantitatively important residue in collagen and a component of reduced glutathione (gamma-glutamyl-cysteinyl-glycine), which is featured in the gamma-glutamyl amino acid transport cycle, was most consistently and severely affected. This study not only indicated that selective reduction in transplacental amino acid transport may be an important factor in intrauterine growth retardation in African Americans, but also confirmed the dietary necessity of the structurally simple amino acid glycine during pregnancy.