The possibility of a relationship between the autosomal recessive mutant gene crinkled in mice and copper metabolism was investigated by examining the effect of copper supplementation during pregnancy and lactation on the expression of the gene in homozygous mutant young. Survival of mutant mice to 30 days of age was doubled by feeding their mothers a high copper diet (500 ppm copper) during pregnancy and lactation, as compared with controls (6-11 ppm dietary copper). High dietary copper also prevented the lag in pigment development characteristic of the mutants. Furthermore, skin and epidermal thickness and hair bulb development were nearly normal in the high copper group, in contrast to thin skin and paucity of hairs in controls. Supplementation with manganese did not have these effects. Scanning electron micrographs showed the presence of three types of hair abnormalities in crinkled mutants, monilethrix, pili torti, and possibly trichorrhexis nodosa. The results show that increased availability of copper favorably altered the expression of the mutant gene, and demonstrate the interaction of a gene and a trace metal in development.