ABSTRACT. Vertebrate fossils from many different formations¯uoresce when exposed to ultraviolet (UV) light. In this paper ®eld observations and controlled experiments in the Chadron Formation (White River Group, late Eocene) of Wyoming are used to assess the utility of searching for fossils at night using ultraviolet light. The results indicate that, especially for very small teeth and egg-shell fragments, searching with ultraviolet light at night can result in signi®cantly more specimens than searching during daylight hours. This method has the potential to increase sample sizes for small vertebrate specimens that are often overlooked when using standard collecting techniques.