Bovine liver, heart and round muscle mitochondria were isolated employing respective preparation methods using high speed centrifugation and compared their activities in terms of NADH oxidation. It was observed that heart and round muscle mitochondrial activities were 30.8-fold and 9.3-fold that of liver respectively. It was obvious therefore that the activities of electron transport from added NADH for bovine round muscle and heart were greater and far greater than that of liver origin respectively.