Rat kidney 203Hg-induced metallothionein (HgMT) was separated on a high performance liquid chromatograph equipped with a gel permeation column and an on-line beta radioactivity detector, in order to obtain the simultaneous measurements of renal MT by UV detection and MT-associated 203Hg by a beta radioactivity detector. Metallothionein was separated in three major species by both UV detection at 254 nm and 203Hg detection, probably due to the presence of mercury and copper. A standard curve was prepared which demonstrated excellent linear correlation between the integrated HgMT peaks area and the quantity of HgMT injected into the column. In contrast to the results with the gel permeation column above mentioned, rat kidney HgMT was separated in four peaks by reversed-phase height performance liquid chromatography.