A model is proposed for a general activated complex AXB in oxidation-reduction reactions involving two metal ions (A) and (B). The symbol (X) would indicate the anions or other groupings which might be present, and which ordinarily would be complexed to the metals separately. The effectiveness of (X) is related to its ability to be oxidized or reduced in itself. In the case that (X) consists of oxidizable anions, the probability of electron transfer from (X) to the oxidizing metal (A) is correlated with the strength (energy) of the bond between (X) and (A). Two previous explanations of the catalytic effect of anions on such reactions are discussed, and some experiments outlined will test the validity of the proposed model.