The kinetics of the reaction, OH + NO2+ M → HNO3+ M (1), have been reinvestigated in order to provide data, using the same apparatus, for a series of third bodies, M. A discharge-flow–resonance-fluorescence technique was used to obtain third-order rate constants in the pressure range 1–5 Torr for M = He, Ar, N2, O2 and CO2. At T= 295 ± 3 K, the values of k1/10–31 cm6 molecule–2 s–1 were He, 16 ± 1; Ar, 16 ± 3; N2, 27 ± 2; O2, 26 ± 7; CO2, 45 ± 10 (95% confidence limit errors; systematic errors could contribute an additional 20% range). Similar investigations of the reaction, OH + NO + M → HONO + M (2), for M = He, Ar and N2 gave values of k2/10–31 cm6 molecule–2 s–1 of He, 6.0 ± 0.3; Ar, 7.4 ± 2.4; N2, 11 ± 1. The implications of the results for the atmospheric chemistry of Earth, Mars and Venus are discussed.