Measurements of the rate of decomposition of water as a function of particle size and concentration of a slurry of fissionable and fertile fuel were made on 10 cc samples of slurry, kept in suspension by a mechanical stirrer, in a nuclear reactor. By passing nitrogen through the slurry during the irradiation, the radiolytic gases were stripped from the slurry before they could recombine. The average particle size of the solids, which contained 10% natural uranium, was varied from 6 to 50 μ in diameter. Concentrations between 300 and 1000 gm/liter were studied. In order to correlate the experimental results, use was made of calculations of the fraction of fission recoil energy that escapes to the fluid in a slurry reactor. The results indicate that the value of G(H2)f, the number of hydrogen molecules measured for every 100 ev of fission recoil energy absorbed by the water is about 2.1. This is also the value for G(—H2O)f , the number of molecules of water decomposed by every 100 ev of fission recoil energy under steady-state conditions in a slurry reactor.