Total vertical column amounts of NO have been derived from infrared solar absorption spectra recorded near sunrise and sunset with the 0.01-cm-1 resolution Fourier transform interferometer at the National Solar Observatory on Kitt Peak (elevation 2095 m, latitude 31.9¿N) on February 23, 1981. The results show an increase in NO concentration in the morning, late afternoon values about 40% higher than in the morning, and a decrease in NO concentration in the morning, late afternoon values about 40% higher than in the morning, and a decrease in NO concentration prior to sunset. The measured diurnal changes in the total vertical column amount are compared with values obtained from time-dependent photochemical calculations.