[en] With the pulse radiolysis technique, a single chain of tetrameric bovine methemoglobin (α2/sup III/β2/sup III/) is reduced, producing a mixture of valence hybrids consisting of α/sup III/α/sup II/β2/sup III/ and α2/sup III/β/sup III/β/sup II/. The oxidation of these partially reduced hemoglobins with ferricyanide was studied. It was found that the rate of oxidation of one of them proceeds 6 to 11 times faster than the other. It is suggested that the fast reacting valence hybrid contains reduced alpha chains