Regulation of the maternal immune response to the fetal allograft is essential for the success of pregnancy and delivery of a well-developed neonate. Numerous mechanisms have been postulated to mediate this. We hypothesised that the potent immunosuppressive molecules TGF-beta1 and IL-10 could contribute to this regulation in the mother and neonate during gestation. In comparison to non-pregnant women, TGF-beta1 and cortisol levels were increased significantly in mid (16-18 weeks) and late pregnancy (>37 weeks, no labour), with levels of both highest in late gestation. In contrast, IL-10 levels were significantly lower in maternal plasma in mid-gestation compared with that from late pregnancy and from non-pregnant women. TGF-beta1, IL-10 and cortisol were all detectable in umbilical cord blood plasma with TGF-beta1 levels significantly decreased in association with labour in contrast to cortisol levels that increased with labour. IL-10 levels in cord plasma were comparable to those of adults and did not change with mode of delivery. Elevated levels of TGF-beta1, but not IL-10, in the maternal and neonatal circulation could have a role in immunoregulation of the maternal response to the fetal allograft as well as growth and development of the fetus.