Abstract. The questions as to the increase in zinc (Zn) contents of kidney and metallothionein (MT) in response to copper (Cu) injection were examined. Each rat was injected intraperitoneally once with 0.9% NaCl or Cu (2, 4, or 6 mg Cu/kg body weight (BW)). After Cu injection, 60.0 – 63.3% of the renal Cu contents and 62.4 – 66.2% of the Zn contents were found in the cytosol. The Cu contents in the cytosol and kidneys increased following the injected amounts in the range of Cu dose of 0 and 4 mg kg BW, and remained unchanged thereafter. Although Zn contents in the cytosol and kidneys of the Cu-injected rats were higher than those of the control rats, they did not increase in response to Cu injection. The distribution profiles of the renal cytosol of Cu-injected rats on a Sephadex G-75 column showed that the amounts of the increased Cu and Zn were attributable to the MT fractions. The Cu concentrations in the MT fractions increased in response to Cu injection. It is interesting that in spite of no change in the Zn contents of the MT fractions with increasing doses of Cu, the Zn concentrations in the MT fractions of Cu-injected rats were higher than the control values. These results indicated that Cu injection could influence Zn contents in rat kidneys, the cytosol and the MT fractions in a dose-effect study.