Kinetic studies of the reactions of 3-pentoxy with NO and O-2 have been performed using laser-induced fluorescence detection of 3-pentoxy radicals. Experiments were carried out at a total pressure of 50 Torr at subambient temperatures. Arrhenius expressions are obtained for the reactions of 3-pentoxy with NO (k(NO)) and O-2 (k(O2)): k(NO) = (5.6 +/- 1.6.) x 10(-13) exp[(7.8 +/- 0.6) kJ mol(-1)/RT] cm(3) Molecule(-1) s(-1) (216-276 K), and k(O2) = (4.1 +/- 1.2) x 10(-15) exp[(2.6 +/- 0.6) kJ mol(-1)/RT] cm(3) molecule(-1) s(-1) (220-285 K). No pressure dependence was observed for either rate constant at 243 K between 50 and 150 Torr. The negative temperature dependence of k(NO) is significantly larger than that of other alkoxy radicals, and this suggests a 298 K rate constant that is only one-third to half those measured for other alkoxy radicals. The small negative temperature dependence of ko, is different from the small positive temperature dependence observed for ethoxy and propoxy radicals but is comparable to that previously observed for 2-butoxy. radicals. The observed temperature dependencies of k(NO) and ko, confound expectations that the kinetics of the reactions of larger alkoxy radicals would be very similar to the kinetics of C-1-C-3 alkoxy radicals.