The amount of metallothinoein was examined in mice after Ehrlich-tumor-cell implantation. The amount of hepatic metallothionein in tumor-bearing mice increased 10-fold 7 days after tumor implantation as compared with control mice. Actinomycin D administration inhibited zinc uptake into liver and hepatic metallothionein synthesis induced in tumor-bearing mice. The increase in hepatic metallothionein content did not appear earlier than 6 days. In other tissues and tumor, an increase in metallothionein content was not observed for 7 days after tumor implantation. However, in tumors from zinc- or cadmium-loaded, tumor-bearing mice, an increase in metallothionein content was observed. The zinc level in the serum of tumor-bearing mice gradually decreased, and the zinc content was one half of the control content 7 days after implantation. Actionmycin D administration inhibited the decrease in serum zinc content. The zinc content of liver was increased as compared with control mice 7 days after implantation, but in other tissues changes in zinc content were not observed. The corticosterone level in the serum of tumor-bearing mice increased 2.5 fold 7 days after implantation as compared with control mice.