Ground-based lidars have been used to detect and identify ground-state (v''=0) hydroxyl radicals (OH) in the mesosphere between about 75 and 85 km altitude. These lidars operate near 308 nm and OH is observed through laser-induced-fluorescence on the A2&Sgr;+-X2&Pgr;(0,0) band. The results expose a valuable global set of nighttime OH observations, since existing long-term lidar data at several NDSC sites contain the (serendipitous) OH information. Results of lidar observations are presented from two mid-latitude sites, one in each hemisphere: Table Mountain (34 ¿N), California, and Lauder (45 ¿S), New Zealand. They show observations of a geometrically thin (~3 km) nocturnal layer of OH near 80 km. For the Table Mountain observations, the derived values for the OH density at 80 km typically are 2-4¿105 cm-3 which is in accordance with model predictions [Dodd et al., 1994>. The temporal behavior of the mesospheric OH signal, following sunset, that was found, supports previous model predictions [Allen et al., 1984> in a qualitative fashion. ¿ 1998 American Geophysical Union