During the past few years the number of satellites carrying neutral gas mass spectrometers for in situ geophysical measurements in the thermosphere has increased significantly. In order to make optimum use of the data thus obtained it is essential to make an intercomparison of the absolute number densities from the various measurements. We therefore performed a direct comparison at 'crossover points' of the orbits of the satellites Esro 4/Aeros A, Esro 4/AE-C, and AE-C/Aeros B in the altitude range 150--300 km, and with few exceptions the agreement is within the experimental errors. This result lends confidence to the use of the broad data base obtained by these satellites since December 1972.