AbstractIn a 5 weeks' study rats were given mercuric, methoxyethyl mercury and methyl mercury alone or together with sodium selenite. The distribution of mercury and selenium among the soluble proteins of liver and kidneys has been investigated by gel chromatography. Estimates of the ratios of the concentration of mercury (selenium) of the soluble proteins to that of the precipitates of liver and kidney homogenates are reported. The ratios seem to decrease when selenium is given concomitant with mercury. When mercuric chloride was given alone, 50 per cent of the mercury content in the soluble kidney proteins was found in the fractions of proteins with a molecular weight similar to that of metallothionein. No mercury could be detected in these fractions when both mercuric chloride and sodium selenite were given.