Rate coefficients (k(3)(7)) for the reaction of OH with HO2NO2 (peroxynitric acid, PNA) in the gas phase were measured in the temperature range of 218-335 K by producing OH via pulsed laser photolysis and detecting it via laser-induced fluorescence. The PNA concentration was measured in situ by UV and IR absorption. The H2O2, HNO3, and NO2 impurities present in the PNA sample were quantified by mass spectrometry and/or UV/IR absorption. The measured value of k(3)(298 K) is (3.4 +/- 1.0) x 10(-11) cm(3) molecule' s(-1). The temperature dependence of k(3) is best described by the relation k(3)(T) = (8.8 +/- 2.6) x 10(-19)T(2) exp[(1130 +/- 20)/T] cm(3) molecule(-1) s(-1). The quoted errors for k(3) are at the 2sigma level and include estimated systematic errors. which contribute the most to this uncertainty. The measured values of k(3)(T) were independent of pressure between 10 and 100 Torr of helium. The branching ratios of the reaction OH + HO2NO2 --> products, for the production of HO2 and HNO3 and of NO3 and H2O2, respectively, were determined to be <10% and <5% respectively, at 298 K. Thus, it was deduced that the main pathway for reaction 3 produces H2O, O-2 and NO2 at 298 K. Our measurements reduce the uncertainties but do not significantly alter the currently calculated impacts of HO2NO2 in the upper troposphere and lower stratosphere. In the course of this study, the rate coefficient for the reaction of OH with H2O2 was measured to be k(4)(7) = (2.9 +/- 1.8) x 10(-12) exp[-(110 +/- 150)IT] cm(3) molecule(-1) s(-1) in the temperature range of 273-356 K.