The incidence of iron-deficiency in children of low socio-economic background is estimated to be approximately five percent. In these children iron-deficiency is associated with behavioral disturbances and an overall impairment of intellectual results in a decrease in the activity of platelet monoamine oxidase (MAO), a major enzyme responsible for the inactivation of the biogenic amine neurotransmitters. Since alteration in the levels of amine neurotransmitters in the CNS are related to a variety of behavioral disorders, it can be inferred that a deficit of MAO activity may be responsible for the impaired behavioral and intellectual performance in iron-deficient children. Accordingly, the purpose of the present investigation was to determine if this enzyme is also decreased in platelets of iron-deficient children. Preliminary results with a small sample population indicate platelet MAO activity is not statistically different in normal and iron-deficient children. These results, if substantiated with a larger sample population, suggest that altered MAO activity, most likely, is not responsible for the behavioral change seen in iron-deficient children. These data indicate that the consequence of iron-deficiency in adults may not be related to a specific or direct effect on MAO but may reflect alteration in composition or enzymatic activities of platelets or their subcellular components.