The influence of the K _ATP ⁺ -channel opener diazoxide on the K⁺ cycle and oxygen consumption has been studied in rat liver mitochondria. It was found that diazoxide activates the K _ATP ⁺ -channel in the range of nanomolar concentrations (50–300 nM, K _1/2 ∼ 140 nM), which results in activation of K⁺/H⁺ exchange in mitochondria. The latter, in turn, accelerates mitochondrial respiration in respiratory state 2. The contribution of K _ATP ⁺ -channel to the mitochondrial potassium cycle was estimated using the selective K _ATP ⁺ -channel blocker glibenclamide. The data show that the relative contribution of K _ATP ⁺ -channel in the potassium cycle of mitochondria is variable and increases only with the decrease in the ATP-independent component of K⁺ uptake. Possible mechanisms underlying the observed phenomena are discussed. The experimental results more fully elucidate the role of K _ATP ⁺ -channel in the regulation of mitochondrial functions, especially under pathological conditions accompanied by impairment of the mitochondrial energy state.