The Shuttle Radar Topographic Mission (SRTM) produced digital elevation models (DEMs) of most of Earth's land surface, but the radar observational geometry resulted in data voids in areas of high relief. Here we test the derivation of elevation from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) nighttime thermal data for the purpose of filling these voids. The method uses the general linear relationship between temperature and altitude as described by the environmental lapse rate. The results for the test area are generally superior to void filling by interpolation, particularly where voids cross ridges or canyons. Errors associated with the approach are identified along with potential improvements.