In children with iron deficiency anemia, bactericidal capacity of polymorphonuclear leukocytes (PMN) and serum opsonic activity were studied. Nitroblue tetrazolium test (NBT), hexose monophosphate (HMP) shunt activation, and myeloperoxidase (MPO) activity of PMN of these cases were also examined. Bactericidal capacity and HMP shunt activation were found to be decreased in iron deficiency anemia ( p less than 0.001). MPO activity, NBT test, and serum opsonic activity were found to be within normal limits. After 1 1/2 months of iron therapy there was an improvement in bactericidal capacity and it returned to a normal level after 3 months of therapy.