Fish with different ecological needs were captured from the northeast Mediterranean Sea to determine metallothioneinlike proteins in their livers. Heat-treated liver samples were run on a column packed with Sephadex G-75 (Sigma, Germany) for subsequent determination of metals, sulfhydryl, and absorbance at 254 and 280 nm. Liver cytosols of Sparus auratus and Mullus barbarus had three heat-stable protein peaks, whereas Mugil cephalus and Atherina hepsetus had two. The third protein peak, containing metallothioneinlike proteins (5000 to 6000 Da), was present in all fish. Only high- and low-molecular-weight proteins contained sulfhydryl and metals. Zinc was the most abundant metal in the metallothioneinlike proteins, whereas cadmium and lead were not detected. The differences in the characteristics of metal-binding proteins among fish indicate that the biological characteristics of fish species should be carefully taken into account concerning natural monitoring studies.