This study was undertaken to examine a possible role of bis(methylmercuric) selenide(BMS) in selenite-induced redistribution of methylmercury in rats. Pretreatment of diethylmaleate(DEM), which depletes tissue reduced glutathione(GSH), completely suppressed the significant increase of BMS produced by selenite injection in the blood of methylmercury-treated rats. Its inhibitory effect was also observed in the kidney and brain. Under the same conditions, the characteristic accumulation in the brain and testis of total mercury induced by selenite was markedly inhibited by DEM pretreatment. Total mercury in these tissues was not altered by DEM alone and BMS in the blood existed in the erythrocytes, but not in the plasma. Thus, it seems likely that the suppressed formation of BMS in the erythrocytes mainly leads to the decreased accumulation of total mercury in the brain and testis.