The purpose of the present study was to compare the time of introduction of the high-fructose low-copper diet on the expression of copper (Cu) deficiency. Weanling male rats were randomly assigned to either a diet containing 62.7% fructose or starch, and 6.0 (F+Cu) or 0.6 (S-Cu) microgram Cu/g diet, respectively, for either 1, 2, or 3 wk before being transferred to a diet containing fructose and inadequate in copper (F-Cu). At week 10, body weight and relative heart size of rats initially consuming the F + Cu diet was inversely related to the week placed on the F-Cu diet, but not for those initially consuming S-Cu. Hematocrit, hepatic Cu concentration and RBC superoxide dismutase activity were significantly lower in rats initially consuming S-Cu when compared to those fed F + Cu. Mortality was greatest in rats switched to the F-Cu diet at weeks 1 and 2 when compared to those switched at week 3 regardless of the type of diet initially consumed. Plasma cholesterol, triacylglycerols, and blood urea nitrogen concentrations were not significantly altered by the type of diet initially consumed or by the time of introduction of the F-Cu diet. It was concluded that changing rats to a F-Cu diet at 1, 2, or 3 wk after weaning did not significantly improve some of the characteristic signs associated with Cu deficiency, but the later that the F-Cu diet was introduced after weaning the greater the chances for survival.