The relationship between free erythrocyte protoporphyrin and conventional indices of iron status was studied in 49 mothers and their infants. Maternal venous blood samples were collected at 34 weeks gestation and at delivery. The corresponding infant blood samples were collected from the umbilical cord and at age 6 weeks. In each case free erythrocyte protoporphyrin, serum iron, total iron binding capacity, and serum ferritin were determined. Cord free erythrocyte protoporphyrin was negatively correlated with maternal ferritin at 34 weeks gestation (p = 0.016) and at delivery (p = 0.014), and with transferrin saturation at delivery (p = 0.026). The infants' haemoglobin concentrations at 6 weeks were significantly negatively related to maternal free erythrocyte protoporphyrin at 34 weeks (p = 0.026) and at delivery (p = 0.026). Cord free erythrocyte protoporphyrin is an index of maternal iron status in the last trimester. Maternal free erythrocyte protoporphyrin in the last trimester predicts the magnitude of physiological anaemia of the infant at age 6 weeks.