The oxidation of toluene by permanganate has been studied as a model for the oxidation of C-H bonds by metal reagents, metalloenzymes, and metal oxide surfaces. In water, the reaction proceeds by hydride (H-) transfer from toluene to a permanganate oxygen, whereas in toluene solution, permanganate abstracts a hydrogen atom (H-.). The ability of permanganate to abstract a hydrogen atom is rationalized on the basis of the strong O-H bond formed on H addition to permanganate. This approach allows understanding and prediction of the rates of hydrogen atom transfer from substrates to metal active sites.