Dietary copper (Cu) deficiency was produced in Swiss albino mice to determine the temporal relationship between depletion of Cu and changes in the cardiovascular and nervous system. Dams were placed on a Cu-deficient diet 4 days after parturition. Half the dams were provided with deionized water and their offspring are referred to as Cu-deficient (-Cu). Half the dams were given cupric sulfate in their drinking water (20 p~g Cu/mL) and their offspring are referred to as Cu-adequate ( + Cu). At 6 weeks of age a sample of the -Cu mice were repleted with CuSO 4. Mice were sampled 1 day after birth and at weekly intervals for 7 weeks. Both + Cu and -Cu mice grew at the same rate; birth weight increased 16-fold at 6 weeks of age. Liver Cu more than doubled between 1 and 7 days of age. At 2 weeks of age -Cu mice were anemic (lower hematocrit and hemoglobin) and had lower liver Cu and plasma ceruloplasmin activity compared to + Cu mice. Liver Fe was not elevated in -Cu mice until 2 weeks after anemia developed. At weaning first signs of altered catecholamine metabolism included elevation of dopamine in both heart and spleen. Norepinephrine concentrations and content, in contrast, were not both lowered in -Cu mice until 5 weeks of age. Heart weight was first elevated in -Cu mice at 6 weeks of age and relative weight (mg/g body wt) at 4 weeks of age. Liver Cu concentration was lower in 1-week repleted mice than in + Cu mice. Anemia preceded the development of cardiac hypertrophy and altered catecholamine levels in -Cu mice.