The metal-binding protein, metallothionein (MT), is induced by selected heavy metals and has appeared promising as a biological marker of metal exposure. Mammalian MT, however, is induced by additional factors such as environmental stresses, and therefore, the use of MT as a biomarker for metal exposure might be premature. Because of the paucity of data concerning the induction of MT following stress in teleosts, the present comparative investigation focused on the influence of cadmium and environmental stresses on MT induction in mice and bluegill sunfish. Following exposure to environmental stresses, significant decreases in zinc and copper were observed in the gill MT-like fraction, as compared to control. In teleost liver, no significant alterations in metal content were observed in the MT-like fraction, as compared to control. These results indicate that the induction of teleost hepatic MT- like proteins appears to be more metal-specific.