Fetal and maternal serum ferritin and cobalamin concentrations were examined in 40 red blood cell-isoimmunised pregnancies undergoing cordocentesis at 18–38 weeks of gestation and the values were compared to those of normal pregnancies. In the red blood cell-isoimmunised pregnancies, the fetal serum ferritin concentration was increased and the cobalamin concentration was decreased, whereas maternal serum ferritin was decreased and cobalamin was not significantly different from normals. There was a significant association between the degree of fetal anaemia and the increase in fetal serum ferritin concentration, but not with fetal serum cobalamin. This study suggests that fetal haemolytic anaemia is associated with iron overload and cobalamin deficienc