A discharge flow reactor coupled to laser-induced fluorescence (LIF) and mass spectrometry has been used to study the kinetics of the reactions of CH3O with NO and NO3. The value of the rate constant for the reaction CH3O + NO --> products at 298 K and at 1 Torr of He has been found to be k = (4.8 +/- 0.4) x 10(-12) cm(3) molecule(-1) s(-1), in good agreement with the literature data. From the kinetic analysis of CH3O by LIF, the reaction CH3O +/- NO3 --> CH3O2 + NO2 (1) has been found to be followed by the reaction CH3O2 + NO3 --> CH3O + NO2 + O-2 (2). Modeling calculations gave for the rate constants of these two reactions, at 298 K, k(1) = (1.8 +/- 0.5) x 10(-12) cm(3) molecule(-1) s(-1) and k(2) = (1.2 +/- 0.6) x 10(-12) cm(3) molecule(-1) s(-1). Comparison with recent Literature data is given, and the atmospheric implication for nighttime chemistry is briefly discussed.