Laser photolysis/laser-induced fluorescence (LIF) is employed to investigate the kinetics of the reactions, OH+CH3NO2, OD+CH3NO2, and OD+CD3NO2 over the temperature range 296-671 K. Photolysis of nitromethane at 266 nm generates OH or OD radicals. Rate constants are independent of pressure over the range 100-300 Torr. The following Arrhenius equations are calculated: k =(1.1±0.4)x10-12 exp[-(2730±290 cal/mol)/RT] cm3 s-1 for OH, OD+CH3NO2 and k =(5.3±2.4)×10-13 exp[-(2860±340 cal/mol)/RT] cm3 s-1 for OD+CD3NO2. A hydrogen atom abstraction mechanism is supported by evidence from isotopic studies, transition-state theory calculations, absence of pressure effects, known energetics, and measured activation energies. Transition-state theory (TST) calculations predict non-Arrhenius behavior as temperatures approach the combustion regime. The TST calculation is fit by the equation, k = 4.37 × 10-20 T2.4 exp(- 340/T) cm3 s-1 over the temperature range 200-2000 K.