Surface modification of TiO2 nanocrystallites in aqueous solution was carried out by reduction of chloroplatinic acid with TiO2 electrons (e(TiO2)(-)). The TiO2 electrons had been generated through electron injection from 2-propanol radicals, hydrogen atoms, and hydrated electrons produced by gamma or pulse radiolysis prior to the addition of the chloroplatinic acid. Upon addition of the latter, Pt-0 clusters are produced by multistep reduction of the chloroplatinic acid on the TiO2 surface. The present work concerns the material balance and chemical kinetics of the Pt-0 mediated reduction of water and H+ to molecular hydrogen by the TiO2 electron. Pt-0 showed no effect on the rate of oxygen reduction, compared to bare TiO2. The effect of surface Pt-0 on increasing photocatalytic yields, claimed by a number of laboratories, is apparently due to electron capture by the Pt-0 rather than electron removal by oxygen.