Reactions of N( 4 S) atoms with NO and H 2 have been investigated using direct detection of N atoms by the atomic resonance absorption technique in a shock tube apparatus, where N( 4 S) is generated by photodecomposition of NO by 193 nm laser radiation behind reflected shock waves. The rate constant of the reaction, N + NO→N 2 + O (1) has been determined using pseudo first-order kinetic analysis to be k 1 = (1.3 ± 0.3) x 10 13 (cm 3 mol -1 s -1 ) over 1600-2300 K temperature range, which agrees very well with the estimation by Baulch et al. [Evaluated Kinetic Data for High Temperature Reactions (Butterworths, London, 1973), Vol. 2]. No (or very small) activation energy of this process was confirmed. Also, the rate constant of the reaction, N + H2→NH + H (2) has been decided by adding H 2 to NO-Ar mixtures; it is k 2 = (2.8 ± 0.2) X 10 14 exp (- Ea/RT) (cm 3 mol -1 s -1 ), where Ea = 33 ± 7 kcal/mol. A quantum mechanical calculation performed in order to determine the mechanism of this reaction suggests that the reaction N( 4 S) + H 2 →NH + H proceeds via a direct abstraction of H atom from H 2 , and it gives calculated activation energy which is in good agreement with the present experiment.