The present study investigates the effects of factors such as birthweight, gestation and infants' sex on serum protein levels of newborn and their mothers. The mean concentration of serum proteins in newborn and their mothers was found to be similar. The levels of albumin were high with a corresponding decrease in the levels of globulins in infants which may be related to placental transfer of these molecules. A study of the relationship between birthweight and levels of maternal serum protein fractions revealed a positive correlation of the maternal albumin and a negative correlation of the maternal gamma component with the birthweight of infants. Premature infants showed higher levels of serum proteins than full-term infants, which may be due to an increased rate of degradation in the latter group. A decrease in the levels of serum proteins was observed in male infants and their mothers.