A zonal wave number one eastward propagating planetary wave observed in the high latitude winter stratosphere with a period near 4 days has been studied by a number of previous authors. Radar observations coupled with stratospheric analyses are here used to demonstrate that this wave, known as the 4-day wave, extends into the Antarctic upper mesosphere. Previous workers have asserted that the wave is a manifestation of the observation of warm pools rotating in the polar vortex, and that the pool seems to behave in a quasi-nondispersive manner. The observation of the 4-day wave in the upper mesosphere presented here appears to validate previous claims that the warm pools are being maintained by wavelike dynamics, rather than simple advection. ¿ American Geophysical Union 1995