The question as to the increase in zinc and copper contents in metallothionein in response to cadmium injection was examined. Each rat was injected intraperitoneally once with 0.9% NaCl or cadmium (1, 2 or 3 mg cadmium/kg b.w.). After cadmium injection, 51.4-60.4% of the hepatic zinc contents were found in the cytosol. Although the zinc contents in the cytosol and livers of cadmium-injected rats were higher than those of control rats, they did not increase in response to cadmium injection. Approximately 56.1-65.6% of the copper contents in the livers were detected in the cytosol. The copper contents in cytosol and livers of cadmium-injected rats did not increase in response to cadmium injection. The distribution profiles of the hepatic cytosol of cadmium-injected rats on a Sephadex G-75 column showed that the amount of the increased zinc was attributable to the MT fraction. Although the zinc contents in hepatic MT of cadmium-injected rats were higher than those of control rats, they did not increase in response to cadmium injection. These results indicate that zinc and copper contents in metallothionein did not increase in response to cadmium injection.