Abstract: Methods and findings are reported from an investigation in rats of the effects of iron deficiency on the activity of various monoamine-metabolizing enzymes in the brain. The behavioral responses of the rats to increased brain 5-hydroxytryptamine (5-HT) and dopamine (DA) receptor stimulation were measured to determine the functional activity of the monoamine neurotransmitter systems. The neurotransmitters 5-HT, DA, and noradrenaline are intimately involved in the regulation of mood and neuronal activity. Effects of iron deficiency on brain neuronal systems need further study.