The zonal average momentum budget in the middle atmosphere (up to 0.1 mbar) is computed for 7 months of satellite observations in order to determine the forcing needed to obtain a balance. This momentum residual includes forcing by waves with small zonal scals, such as gravity waves. The results indicate that the forcing needed in the lower mesosphere reaches peak values of about 20 m s-1 d-1, which is large compared to the Rayleigh friction used in that part of the atmosphere in numerical models, such as that of Holton and Wehrbein (1980a). The seasonal change follows that of Rayleigh friction; the northern hemisphere momentum deficit is large easterly in winter, decreases in the spring, and becomes small westerly in late spring. However, the largest momentum deficits are in middle and high latitudes (50¿--80¿N) in winter, whereas the largest Rayleigh frictional damping is in the vicinity of the jet (30¿--50¿N). The observations were also compared with the parameterized acceleration of the mean flow by gravity waves (Lindzen, 1981; Holton, 1983). The observations of the wintertime momentum residual are similar to the values used in the circulation model of Holton (1983). Derivation of the parameterization constant from the satellite observations results in an equivalent zonal wave number for gravity waves that is substantially smaller than that used by Holton (1983) in his model. Possible reasons for this difference are that many of the gravity waves break at levels above the region where data are available and that gravity with nonzero phase speeds may be present.