We report an experimental assessment of the contributions of the shockwave and the hot channel to the production of nitric oxide by simulated lightning. Lightning in the laboratory was simulated by a hot plasma generated with a pulsed Nd-YAG laser. The temporal evolution of electric breakdown in air at atmospheric pressure was studied from the nanosecond to the millisecond time scale by shadowgraphy and interferometry techniques. The shock-wave front velocity was determined to be about 60 km s-1 at 20 ns and the temperature behind the shock front was estimated to be about 105 K. The production yield of nitric oxide by shock heating is estimated to be: P(NO) (3¿2)¿1014 molecule J-1. In contrast it was calculated that the production yield of NO by the hot channel is as much as P(NO)=(1.5¿0.5)¿1017 molecule J-1. To the extent our simulation is an accurate representation of natural lightning, the hot channel is the dominant region for nitrogen fixation. ¿ 2001 American Geophysical Union