Studies of uptake and release of 64Cu, 109Cd, and 65Zn in suckling C57BL/6J male mice revealed kinetics and distributions that differed for each metal both within and among the organs analyzed, suggesting distinct, albeit overlapping, mechanisms for transport and binding of each metal. In mutants, there were tissue-specific increases in copper-binding capacity. In hemizygotes (Moblo/y) accumulation of 64Cu was increased in kidney, lung, and duodenum. In heterozygotes (Moblo/+), 64Cu content was increased in kidney, with a smaller increase in lung, and no change in duodenal Cu. Decreased 64Cu accumulation was seen in liver in both hemi- and heterozygotes. In contrast, 64Zn and 109Cd accumulation in organs of heterozygote mice was not significantly distinguishable from normal. In skin and connective tissues there is excessive accumulation of 64Cu in Moblo/+ and Moblo/y, no abnormality in heterozygote 65Zn accumulation, but a clear decrease in heterozygote 109Cd content. In both mutant kidney and liver, there was an aberrant subcellular distribution of 64Cu, with the major fraction of sequestered 64Cu in the cytosol. Our studies establish that in spite of the ubiquity of metallothioneins and the structural similarities of those that have been characterized, there is specificity and functional heterogeneity in metal binding among tissues. The aggregate data suggest that there are unique regulatory mechanisms for the metabolism of copper and zinc, while there exists, in part, an inverse relationship between the binding of copper and cadmium. Our data further suggest that the blotchy mutation involves a specific cytosolic copper storage or transport protein also capable of binding cadmium.