Radiolysis kinetics in NO3- and NO2- solutions during gamma-irradiation were studied at an absorbed dose rate of 2.1 Gy center dot s(-1) at room temperature. Air- or argon-saturated nitrate or nitrite solutions at pH 6.0 and 10.6 were irradiated, and the aqueous concentrations of molecular water decomposition products, H-2 and H2O2, and the variation in the concentrations of NO3- and NO2- were measured as a function of irradiation time. The experimental data were compared with computer simulations using a comprehensive radiolysis kinetic model to aid in interpretation of the experimental results. The effect of nitrate and nitrite, present at concentrations below 10(-3) M, on water radiolysis processes occurs through reactions with the radical species generated by water radiolysis, (center dot)e(aq)(-), O-center dot(2)-, and (OH)-O-center dot. The changes in H-2 and H2O2 concentrations observed in the presence of nitrate and nitrite under a variety of conditions can be explained by a reduction in the radical concentrations. The kinetic analysis shows that the main loss pathway for H-2 is the reaction with (OH)-O-center dot and the main loss pathways for H2O2 are reactions with (center dot)e(aq)(-) and (OH)-O-center dot. Nitrate and nitrite compete for the radicals leading to an increase in the concentrations of H-2 and H2O2. Post-irradiation measurements of H-2, H2O2, NO2- and NO3- concentrations can be used to calculate the radical concentrations and provide information on the redox conditions of the irradiated aqueous solutions.