Comparative metabolic fate of labelled chromium chloride and sodium chromate and interaction of these compounds in the rat liver and blood were investigated after their oral and intravenous administration. Gastrointestinal absorption of both compounds was below 1% of the oral dose, but trivalent chromium showed higher radioactivity than the hexavalent form in rats (biological half-life : CrCl₃ 91.79 days, Na₂CrO₄ 22.24 days). The higher residual activity of the trivalent chromium was also observed after intravenous administration. Both forms of chromium were excreted more in the urine via the kidney than in the intestinal tract after intravenous administration. When ⁵¹CrCl₃ and Na₂⁵¹CrO₄ were injected into rats, in the time-distribution patterns of ⁵¹Cr in the organs, a significant difference was shown between oxidation states of the two compounds, especially in subcellular fractions of the liver and blood constituents. This significant difference mainly observed in the rat blood came from the fact that trivalent chromium possessed a high binding activity for transferrin in plasma, while hexavalent chromium was permeable into red cells and bound with hemoglobin.