We review the evidence for H+ translocation by reconstituted cytochrome c oxidase; attention is paid to those aspects which we feel most open to criticism. Possible alternative hypotheses are assessed, with regard to experiments carried out to test them directly and with regard to published data. We conclude that, whilst certain aspects of this system are worthy of further clarification, the reported observations are all consistent with proton translocation by reconstituted cytochrome c oxidase; most of these observations provide a positive indication of such an activity.
