The effect of inhibitors and activators (channel openers) of ATP-regulated potassium channel on potassium ion transport was studied in isolated rat liver mitochondria. In order to follow the potassium transport into mitochondrial matrix light scattering measurements have been employed. The membrane potential of rat liver mitochondria, upon addition of potassium channel openers, was measured with the use of TPP-ion selective electrode. The results show that some of the potassium channel openers like HOE 234 and Y27152 are able to activate potassium transport into mitochondria. On the other hand, mitochondrial potassium uniport found was inhibited by the antidiabetic sulfonylureas and was not affected by other potassium channel inhibitors like 4-amino pyridine.