The metallothionein(MT)was purified from the liver of Carassius auratus induced by exposure to cadmium chloride and characterized.It shows very similar to mammalian metallothioneins in all of its properties.The MT of the fish contains high cysteine contents(30%)and with an absence of aromatic acid residues.The thiol groups of the cysteine residues combine with the cadmium in SH/Cd molar ratio of 3∶1 and produce a characteristic absorption maxium at 250 nm,minimum at 280 nm.The metal analyses reveal only traces of zine and copper in addition to cadmium. The molecular weight is determined to be about 10 000 by gel filtration on HPLC and SDS-PAGE method. The isoelectric point of fish MT is demonstrated to be about 5.6.