Two forms of liver metallolthioneins were isolated and purified skipjack, using saltingout on ammonium sulfate, gel-filtration on Sephadex G-75 column, DEAE-Sephadex A-25 ionexchange chromatography, and gel-filtration on Sephadex G-50 column. The homogeneous state as judged by polyacrylamide disc-gel electrophoresis was achieved. The molecuar weight of the two metallothioneins, D2 and D3, was estimated to be about 11, 200, this was determined by gel-chromatogrphy on Sephadex G-50 column. The metallothioneins D2 and D3 are composed of 103 and 104 amino acid residues, respectively, and their amino acid compositions are quite similar. Their distinctive features include an extremely high content of cysteine, which is about 30% of all amino acid residues, and the absence of aromatic amino acid histidine, and arginine. The total metal contents of cadmium, copper and zinc in D2 and D3 are 9 and 10 atoms per molecule respectively.