Over the 3-day period from 12 to 14 October, 1990, the sodium abundance in the lunar atmosphere at 80¿ South increased by 60%, while interspersed measurements at the equator showed no substantial change. The source is suggested to be an unknown meteor shower with a radiant near the south ecliptic pole. A low relative velocity of ~20 km/sec, combined with a small particle masses, would keep the shower below the detectability threshold of radar. The stream could evolve from a reasonable asteroidal or cometary orbit with perihelion somewhat greater than 1 astronomical unit (AU) and a major axis of a few AU. The short residence time of lunar sodium makes it more favorable than the terestrial sodium layer for detection of such an event. ¿American Geophysical Union 1991