A comparison of the diurnal component of the daily variation in the neutral composition data from the San Marco 3 Nace (Neutral Atmospheric Composition Experiment) mass spectrometer at 220, 250, and 280 km, the Ogo 6 model data at 450 km, rocket measurements of nitrogen between 140 and 300 km, and the two-constituent theoretical model of Mayr and Volland (1973) gives good agreement for molecular nitrogen and atomic oxygen. The Nace and rocket measurements overlap in altitude, and there is good agreement in the amplitude and phase of the diurnal and semidiurnal components for molecular nitrogen, suggesting that the predominant semidiurnal mode above 220 km may be a P22 mode. The helium diurnal amplitude and phase of the theoretical model is in fair agreement with the Nace results, while the amplitude from Ogo 6 model at 450 km is much larger than the model predicts, a result suggestng that the Ogo 6 model diurnal amplitude may be overestimated as the result of an incompletee separation of local time and seasonal effects.