Specific effects of various catecholamines as well as functional dependence of mitochondrial enzymes activity on catecholamine metabolism were studied. Dopamine activated cytochrome c oxidase in heart mitochondria and decreased this enzymatic activity in liver tissue. Noradrenaline and adrenaline activated cytochrome c oxidase in liver, brain and kidney tissues. The effect of dopamine on cytochrome c oxidase was prevented by activation of dopamine beta-hydroxylase. Increased activity of monoamine oxidase caused accumulation of catecholamine metabolites, which inhibited the succinate dehydrogenase activity in liver tissue and the cytochrome c oxidase activity in brain, kidney and liver tissues. In the catecholamine regulation of succinate dehydrogenase and ATPase activities in all the tissues studied as well as of cytochrome c oxidase activity in heart tissue the quinoid oxidation products were apparently involved.