The problem of electron transfer phosphorylation was first formu- lated in 1939 by Belitser and Tsibakova I who introduced the P: 0 criterion and showed that this ratio is more than 1. The authors ted that such a high value of the phosphorylation coefficient suggests a fundamental difference in the mechanisms of A TP formation coupled with respiration, and glycolysis, since in the latter case, the amount of the ATP synthesized is equal to that of the substrate utilized. A lot of hypothetical schemes were put forward to explain the nature of coupling between electron transfer and phosphorylation, but ne of them solved the problem. Only quite recently, one hypo- thetical scheme of energy coupling, viz. Mitchell's chemiosmotic concept, 2.3 was supported by experimental data which allow us to prefer it to alternative possibilities. In this paper, I shall try to substantiate the statement that oxidation and phosphorylation can be coupled via a membrane potential as was postulated by Mitchell.