1. In -γ-radiolysis of aqueous solutions of nitrotetrazolium salts, the yield of formazane in a neutral medium is higher than that for 2,3,5-triphenyltetrazolium chloride. The yields of formazanes increase in alkaline medium and in the presence of OH radical acceptors. 2. A correlation between the values of the rate constants of the reactions of the CO2− radicals with tetrazolium salts and the half-wave potentials of the reduction of these salts was established.