The effect of PRP on the Mg²⁺-, Ca²⁺- and HCO₃^- - dependent ATPase activities in the mitochondria isolated from 1- and 6-month old rat brain and liver was studied. It was shown that mitochondria isolated from the mentioned tissues of 1-month old rats possessed relatively high ATPase activity in compare with that of 6-month old ones. A significant elevation of various ATPase catalytic activities was observed in the mitochondria isolated from the brain as well as from the liver. This elevation was more intensive in the mitochondria of 6-month old animals in compare with that of 1-month old ones. It may be concluded that PRP developed a selective effect on the ATPase catalytic activity expressing a definite age dependence.