Cytochromes a₁⁵⁹⁰, b⁵⁶⁰, c₁⁵⁵⁴ and c₁⁵⁵² were isolated and purified from a strain of Acetobacter suboxydans. The procedures used were described in detail.The main cytochrome band at 550-560 mμ in intact cells splitted at liquid air temperature into two bands, 551 mμ (strong) and 559 mμ (weak).Optical and physiological properties of the four cytochromes were investigated. Lactic dehydrogenase activity was found to be associated with cytochrome c₁⁵⁵⁴. The two c₁-type cytochromes, especially cytochrome c₁⁵⁵⁴, persisted in their reduced form after the purification through many steps.By some combinations of isolated components reconstruction of the oxygen uptake system could be realized.The oxygen-consuming activity of purified oxidase preparations was accelerated by a-tocopherol but not by Emasoll 4130 and Tween 80.Some discussions were made on the nature of terminal oxidase, the role of cytochrome c₁⁵⁵² in the electron-transport system, and persistence of reduced state of c₁-type cytochromes.A possible scheme of the electron-transferring system of Acetobacter suboxydans was presented.