In the untreated infant with Menkes Kinky Hair Syndrome, copper concentrations in brain and liver are deficient, while excessive copper accumulates in other tissues. The observed serum ceruloplasmin response after parenteral copper administration is suggestive of an impairment in the incorporation of copper into this metalloprotein. These findings, together with increased urinary copper excretion and the absence of clinical improvement, are compatible with a generalized defect in copper metabolism, transport or storage. The excessive accumulation of copper in many tissues illustrates the potential danger of parenteral copper therapy.