Kwashiorkor may occur when an imbalance between pro- and antioxidants in malnourished children results in an excess of free radicals. The concentrations of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), reduced glutathione (GSH) and glutathione peroxidase (GPX) were measured in erythrocytes of 22 children with kwashiorkor on admission to hospital and repeated on days 5, 10 and 30 of recovery. The concentrations were compared with those in 22 children with marasmus and in 20 children who were normally nourished but had infective illness necessitating their hospitalization. CAT and SOD were similar in all groups and did not change during recovery. GSH and GPX were significantly lower in kwashiorkor than in the other groups. Concentrations of thiobarbituric acid-reactive substances (TBARS), a marker of lipid peroxidation, were significantly elevated in children with kwashiorkor. During clinical recovery, GSH but not GPX concentrations rose despite an increase in plasma selenium levels and decreased concentrations of TBARS. These findings suggest that the antioxidant status of children with kwashiorkor differs from that of well nourished and marasmic children. Whether these differences are the cause of the consequence of the clinical picture is unresolved.