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Recent evidence from several laboratories suggest the existence of a direct, intramembranal, proton pathway between the redox H+-pumps and the ATPase H+- pump in addition to the bulk to bulk pathway [reviewed in Rottenberg (1985), Ferguson (1985) and Westerhoff et al. (1984)]. We have suggested previously that collisions and dynamic aggregation of the mitochondrial inner membrane proteins enhance direct intramembranal proton transfer and thus energy conversion (Rottenberg 1978, 1985). We have shown previously that ambient temperature strongly affects the degree of coupling of oxidative phosphoiylation in rat liver mitochondria. In high temperatures there is a significant reduction of both the respiratory control (Rottenberg, 1978) and the State 4 phosphate potential, ΔGp (Rottenberg et al. 1985). This reduction of respiratory control and phosphate potential at elevated temperatures is not due to reduction of Δμ H which, in fact, increases slightly at elevated temperatures (Rottenberg et al. 1985). Thus, despite an increase in Δμ H, the efficiency of coupling, as reflected in the ΔGp/Δμ H ratio, is decreased (Fig. 1, Rottenberg et al., 1985). Moreover, in liver mitochondria isolated from ethanol-fed rats (in which the concentration of the redox and the ATPase H+- pumps are greatly reduced), the ratio ΔGp/Δμ H is reduced at all temperatures even though Δμ H is the same as in control rats. These data are compatible with the suggestion that efficient energy conversion depends on the frequency of collisions and the extent of dynamic aggregation of the inner membrane proteins.