Fifty low birth weight babies (both preterms and intrauterine growth retarded) and their mothers were the subjects of the study. Ten fullterm babies weighing more than 3.0 kg and their mothers served as controls. The cord serum IgG levels were significantly lower in preterm babies compared to fullterm appropriate for gestational age (FT-AGA) and fullterm intrauterine growth retarded (FT-IUGR) babies. The cord serum IgG levels were not significantly different between FT-AGA and FT-IUGR babies. The maternal serum IgG levels were significantly higher than the cord serum IgG levels in preterm group whereas in fullterm AGA and IUGR groups cord serum IgG levels were significantly higher then the maternal serum IgG levels. There was no correlation between maternal and cord serum IgG levels. The cord serum IgG levels were significantly correlated with gestation even after controlling birth weight. The correlation between cord serum IgG levels and birth weight disappeared once qestation was controlled.