Red cell superoxide dismutase activity was determined on cord blood samples. The normal range of activity in neonates, measured per gram of haemoglobin, was lower than that obtained for adults, with the mean value for neonates being approximately two‐thirds of the adult level. When activity was measured on a per cell basis it was still lower than the adult level. Adult levels are reached at approximately three months postnatal age. No correlation was found between low superoxide dismutase activity and prematurity, low birthweight. Apgar, respiratory distress syndrome, or se