The resonance absorption method is described for detecting ppm concentrations of NO mixed with other gases. As source lamp for the emission of the NO γ system, A2 ∑+- X 2∏, a hollow cathode discharge has been used operating in streaming air at low discharge current (∼). NO detection is achieved by a double-beam technique with single-beam optics. The experimental average absorption coefficient obtained for the γ (0,0) band is compared with the calculated value. Relevant NO spectroscopic information is reported.