The reactions of methylperoxy radicals with NO3 and NO were investigated at room temperature using the method of discharge flow/mass spectrometry, For reaction with NO, data were obtained for normal and deuterated methylperoxy. k(CH3O2 + NO) = (7.5 +/- 1.0) x 10(-12) cm(3) molecule(-1) s(-1) and k(CD3O2 + NO) = (8.6 +/- 1.0) x 10(-12) cm(3) molecule(-1) s(-1). The rate constant for reaction of CD3O2 with NO3 was found to be k(CD3O2 + NO3 --> CD3O + NO2 + O-2) = (1.3 +/- 0.2) x 10(-12) cm(3) molecule(-1) s(-1). In addition, rate constants were obtained for the reaction of CD3O with NO3 : k(CD3O + NO3 --> CD3O2 + NO2) = (3.7 +/- 0.8) x 10(-12) cm(3) molecule(-1) s(-1), k(CD3O + NO3 --> DCDO + DNO3) = (5.6 +/- 1.0) x 10(-13) cm(3) molecule(-1) s(-1).