The initial yield of molecular hydrogen in [gamma]-irradiated aqueous solutions has been measured as a function of acidity in the range from neutral solution to 10 [image] sulfuric acid. The observed decrease in the hydrogen yield with increasing acidity is explained with the assumption that the gross number of radicals formed per unit absorbed dose is independent of pH, so that the increase in measured radical and peroxide yields in acid solutions must occur at the expense of the hydrogen yield and the yield of recombined unlike radicals to form water.