Global grids have been constructed from high-quality TIROS-N microwave sounder unit measurements which closely approximate the 30- to 150-mbar geopotential thickness. The grids compare favorably with conventional analyses. Grids for January 1979 are spectrally analyzed by Fourier transform for zonal wave numbers 1-10 over latitudes 80¿N to 80¿S. Both time mean and trasient medium-scale waves are discussed in some detail. In the time mean, wave 1 dominates all northern latitudes. In equatorial regions, wave 1 also is dominant, but a secondary spectral peak is noted at wave 4. The most remarkable feature seen is a strong medium-scale structure with eastward movement in southern (summer) mid-latitudes. Zonal wave numbers 5 and 6 have periods of about 10-15 days and 5 days, respectively. These results provide independent corroboration of such structures recently reported by several investigators. The mechanism by which the dominant medium-scale waves are maintained is not understood.