Lidar measurements of mesospheric Fe were conducted at Urbana, IL (40¿N, 88¿W) during 4 nights in late October 1989. The average Fe abundances, layer centroid heights and rms widths varied between 1.0-2.0¿1010 cm-2, 89.0--90.5 km and 3.2--4.1 km, respectively. The peak densities of the layer near 90 km varied between 15-25¿103 cm-3. Considerable gravity wave and tidal activity was observed in the Fe profiles. On 3 nights the formation and dissipation of 3 large sporadic Fe (FeS) layers was observed. These are the first observations of this phenomenon. The 2 largest FeS layers formed at 102.4 km and 91.4 km over a period of about 20 min and their widths were approximately 2.3 km FWHM. The peak densities of the FeS layers were as high as 31¿103 cm-3 and the abundances were as high as 5.8¿109 cm-2. The observations are compared with previous measurements of mesospheric Fe and with recent observations of sporadic Na (NaS) layers. ¿ American Geophysical Union 1990