High-resolution radar and lidar measurements of sporadic sodium (Nas) and sporadic E (Es) layers were made at the Sondrestrom incoherent-scatter radar facility on 11 December 1997. These measurements suggest a causal link between Es and Nas, supporting the proposed mechanism in which Na+ ions in the Es are neutralized to form the Nas. This Nas, by contrast, does not appear to have been formed by the presence of auroral precipitation or ionization, and, in fact, the sodium density is seen to decrease during an auroral event. ¿ 1998 American Geophysical Union