The subcellular localization of Se and Hg and their cytosolic binding proteins, including cellular oxidative status, in porcine liver and kidney have been studied by using samples from a chronic Hg-contaminated area and a non-Hg-contaminated area. Coaccumulation and redistribution of Se and Hg in subcellular fractions due to mercury exposure were found. The Hg and Se concentrations in tissues from Hg-exposed porcine were 80 fold and 5-20 fold higher than controls, respectively. Interestingly, the retention of both Se and Hg increased 10% in mitochondria, while decreased 10% in cytosol of Hg-exposed pig liver. Mercury was mainly in the form of MTs in the cytosol of the non-Hg-exposed porcine kidney. MT binds Hg in the cytosol with limited capacity, and the rest Hg was redistributed to the high molecular weight (MW) proteins (80-100 kDa) in the Hg-exposed group. The coaccumulation of Hg and Se was also found in high MW proteins, where their molar ratio tended to be 1:1. Moreover, the Se-containing polypeptides (3-6 kDa) increased significantly both in hepatic and renal cytosol of the Hg-exposed pigs. Se-dependent GSH-Px and SOD activity were increased to cope with Hg-induced oxidative stress. In previous studies, the roles of Se and MTs were generally taken into account separately; we discussed their combining roles in the case of high Hg exposure. The present results were beneficial to understand the existing states of Hg in vivo and evaluate the interaction of toxic and essential elements.