A metallothionein-I-transgenic mouse strain (MT-TG) was characterized to determine whether they would be suitable to study the functions of this protein. MT-TG mice were visually indistinguishable from nontransgenic littermate controls, but had 10- to 20-fold higher basal levels of MT protein in pancreas, liver, and stomach, as well as 2- to 6-fold higher MT protein levels in other organs (kidney, intestine, uterus, testes, spleen, heart, and lung) than control mice, as determined by the Cd/hemoglobin assay. The MT-TG mice had 50% more Zn in liver and 300% more Zn in pancreas than control mice. Interestingly, female MT-TG mice have 4- to 5-fold higher MT levels in liver than those of males. To determine whether MT can be further increased by well-known MT inducers, control and MT-TG mice were given Zn (200 μmol/kg), Cd (20 μmol/kg), or diethyl maleate (DEM, 5 mmol/kg), and tissue MT concentrations were measured 24 hr later. MT-TG mice responded to MT inducers in a manner similar to control mice. The hepatic antioxidant components (glutathione (GSH), GSH-peroxidase, GSH-reductase, GSH S-transferase, superoxide dismutase, DT-diaphorase, and catalase) of MT-TG mice were not different from those of controls. The cytochrome P450 enzymes (total P450, b₅, NADPH cytochrome c reductase) were normal in these MT-TG mice. The activities of CYP1A, CYP2B, and CYP2E enzymes in MT-TG mice were also similar to those of controls, as determined by ethoxy- and pentoxyresorufin O-dealkylation and chlorzoxazone 6-hydroxylation. Thus, MT-TG mice appear to be a good model for studying functions of MT.