The serum concentration of cytoferrin, a low-molecular-weight iron-binding compound, in an infant with neonatal hemochromatosis was significantly elevated (270X) by comparison with normal adult values. Concentrations of cytoferrin in cord sera from 25 normal term neonates were substantially lower but also were elevated (2X) by comparison with normal adult values. Concentrations of cytoferrin in placental tissues were comparable to values previously obtained for various mammalian tissues, and concentrations of cytoferrin in maternal sera were not elevated. This transplacental gradient in serum concentrations of cytoferrin suggests that cytoferrin may be involved in maternofetal iron transport. Although iron is known to be taken up by the hemochorial placenta via trophoblast brush border receptors for transferrin, further iron handling within the placenta is poorly understood. In particular, the routes or carriers by which iron enters the fetal circulation have not been identified. Cytoferrin may participate in stages of maternofetal iron transport distal to transferrin, and further investigation of the role of cytoferrin in neonatal hemochromatosis and other disorders may be warranted.