The mesospheric sodium layer was measured for 42 nights during the period from April to October, 1985, at Syowa Station (69¿00' S, 39¿ 35' E), Antarctica, by using a dye laser radar (lidar) tuned to the D2 line of sodium. This observation was made as part of the Middle Atmosphere Program (MAP). In contrast to the results obtained at mid-latitudes in the northern hemisphere, the seasonal variation in abundance showed no significant winter maximum. Further, there was no apparent seasonal variation in the vertical distribution of sodium density. However, we observed oscillatory variations in abundance with a period of about 40 days. The nocturnal variations in the sodium density profile have a wavelike structure with a vertical wavelength of 10 to 16 km and a period of 3 to 8 hours, which suggests strongly that gravity waves are propagating upward through the sodium layer. The sodium lidar measurements during auroral activity give evidence that the layer is disturbed associated with the auroral breakup event. ¿American Geophysical Union 1987