During the early morning of January 16, 1989 the Arecibo 430 MHz incoherent scatter radar and the University of Illinois CEDAR Na lidar were operated simultaneously for several hours at the Arecibo Observatory, Puerto Rico (18¿N, 67'W). At approximately 0425 LST a sporadic E (ES) layer began forming near 101 km altitude and moved steadily downward reaching an altitude of 99 km by 0500 LST. The electron abundance of the ES layer increased rapidly from approximately 3¿109 cm-2 at 0510 LST to approximately 6¿109 cm-2 by 0530 LST. During this same time period a sporadic Na (NaS) layer formed at the same altitude as the ES layer. Both the ES and NaS layers moved upwards together between 0530 and 0600 LST before dissipating at an altitude of 101 km. The high correlation between the altitude and abundance variations of the two layers strongly suggests that the NaS layer formation is related to the ES layer and may involve Na cluster ion chemistry. ¿ American Geophysical Union 1989