ApoLPHD and apoLPVLD affected the oxidative phosphorylation in mitochondria isolated from liver tissue of starved and intact rats depending on the dose administered; apoLPHD exhibited a partial effect, apo LPVLD--caused complete uncoupling of respiration and phosphorylation. Low concentrations of the both apoproteins increased the rate of mitochondrial respiration at the metabolic states 3 and 4 and did not alter the rate of phosphorylation. The additive effect was not observed after addition of dibutyryl-cAMP simultaneously with apoLPHD or with apoLPVLD into the incubation samples at low doses causing no uncoupling action. Under these conditions the effects of apoproteins prevailed. The apoproteins appear to participate in adaptive modifications of oxidative metabolism in stress-impaired liver mitochondria.