The mutual effects of Cd(2+) and ruthenium red on rat liver mitochondrial energy transfer reaction are described. In results, ruthenium red recovered the depression of the oxidative phosphorylation induced by Cd(2+). Ruthenium red suppressed the K(+) release induced by Cd(2+). As the binding site of the Cd(2+) have other than the binding site of ruthenium red, the site of ruthenium red is greatly related with the inhibitory effect of Cd(2+) and this site is similar to the binding site of Ca(2+).