The resemblance between fetal growth retardation (FGR) and malnutrition acquired postnatally is striking. The similarities include suboptimal physical development (including retarded bone age), loss of subcutaneous fat, dry skin with reduced turgor, hypoglycemia, hypothermia, frequent and severe infections, and high mortality. In addition, restriction of growth during fetal life is. associated with perinatal asphyxia, minimal postnatal weight loss, polycythemia and elevated levels of erythropoietin, and increased incidence of congenital malformations. Increased frequency of infection in such infants is an established clinical observation. Failure or impairment of immune defense mechanisms of infants with FGR is, therefore, suspected as a basis for the susceptibility of such infants to infection. Heretofore, there have been no comprehensive systematic analyses of the effect of fetal malnutrition on postnatal immunocompetence, unlike undernutrition acquired after birth for which considerable data are now available.1-4 The following is a summary of our recent studies relevant to this problem.