The first successful measurements of nitric oxide band absorption in the earth's atmosphere have been made by using the high-resolution ultraviolet spectrometers on Orbiting Solar Observatory 8. These measurements were concluded between January and August 1977 and between 30 ¿ north and south latitudes. The nitric oxide absorption data, at the (1, 0) delta band wavelength of 1829.41 ¿, are numerically inverted to produce nitric oxide density profiles between 85 and 145 km. The major finding of the observations is that for altitudes below 95 km there is more nitric oxide at sunrise than at sunset. A numerical model, incorporating time-dependent ionospheric chemistry and vertical diffusive transport (both eddy and molecular), is used to simulate the Oso 8 nitric oxide profiles. The peak of the model sunset profile lies at 95-km altitude, in agreement with observation, if the vertical component of the eddy diffusion coefficient is 107 cm2 s-1 near 100 km. The model specifies a sunrise to sunset density ratio of 1.9 at 85 km, while the observed value is 4.2+7.3-2.7. Vertical and horizontal transport processes are probably responsible for the observed diurnal variation.