We have compared serum galactosyltransferase activity in pregnant women and in newborn children. Subjects in this study were 75 women at different stages of pregnancy and 60 newborns, including premature infants. Activity ratios in pregnant women are based on the period of gestation, expressed in weeks of amenorrhea. Average values were 265 nmol/h/ml for up to 12 weeks of amenorrhea, 369 from 13 to 28 weeks and 483 over 28 weeks versus 232 nmol/h/ml for non-pregnant women. In infants, galactosyltransferase activity decreased with increasing age from conception, but the activity level was always much higher in newborns than in women at the ninth month of pregnancy. We discuss the origin of the enzyme in these various samples.