Cognitive function. There is reasonably good evidence that mental and motor developmental test scores are lower among infants with iron deficiency anemia. Although the research on cognitive function in iron deficient older children and adults is sparse and diverse, it suggests that there may be alterations in attentional processes associated with iron deficiency. Iron therapy has not yet been shown effective in completely correcting many of the observed disturbances. Although some aspects of cognitive function seem to change with iron therapy, lower developmental. I.Q., and achievement test scores have still been noted after treatment. The behavioral effects of iron-deficiency anemia may be due to changes in neurotransmission. However, the biochemical bases are not yet completely understood. Noncognitive disturbances. A variety of noncognitive alterations during infant developmental testing has also been observed, including failure to respond to test stimuli, short attention span, unhappiness, increased fearfulness, withdrawal from the examiner, and increased body tension. Exploratory analyses suggest that such behavioral abnormalities may account for poor developmental test performance in infants with iron deficiency anemia. These studies indicate the fruitfulness of examining noncognitive aspects of behavior such as affect, attention, and activity, in addition to specific cognitive processes. Activity and work capacity: There has been a steady accumulation of evidence that iron-deficiency anemia limits maximal physical performance, submaximal endurance, and spontaneous activity in the adult, resulting in diminished work productivity with attendant economic losses. The relative importance of central and peripheral mechanisms underlying these effects, the extent to which anemia or iron deficiency separate from anemia is responsible, and the counterpart in infants and children remain to be established. This essay has examined recent evidence from research on central nervous system biochemistry and from human studies that iron deficiency adversely affects behavior by impairing cognitive function, producing noncognitive disturbances, and limiting activity and work capacity. The body of research taken as a whole provides increasingly persuasive arguments for intensifying efforts to prevent and treat iron deficiency anemia.