An effective rate coefficient for N2++0→NO++N which increases with altitude is deduced from an analysis of the auroral ion composition measured between 120 and 200 km over Poker Flat, Alaska on March 6, 1981. This result may be interpreted in terms of a rate coefficient with a positive temperature dependence, roughly k3?1.5¿10-10 (Ti/3000)0.6 cm3 s-1 over a 300-1600 ¿K temperature range. Other interpretations are discussed, including the possibility that the N2+ ions are vibrationally excited.