As part of the U.S. Environmental Protection Agency's effort to develop and demonstrate a reliable model of atmospheric dispersion for pollutant emissions in irregular mountainous terrain, the Complex Terrain Model Development Program was initiated. The first phase, a comprehensive tracer field study, was carried out on Cinder Cone Butte, Idaho, during the autumn of 1980. Eighteen quantitative tracer experiments were conducted, each lasting 8 hr at night or early morning. The main tracer gas was sulfur hexafluoride; a second tracer, Freon 13B1 was used in ten of the eighteen experiments. Averaged meteorological data were recorded from six towers near and on the slopes of the hill. Data consisted of direct and derived measures of temperature, wind, turbulence, solar and net radiation, and nephelometer coefficient of scattering. Hourly wind profiles were obtained from pilot balloon observations; tethersonde observations recorded profiles of wind and temperature. Tracer gas concentrations were detected by a network of approximately 100 samplers located on the slopes of the hill. The system used to collect the data, the operation procedures used to run the system, and its performance record are described. Tables of tracer gas release data have been included to assist in any modeling effort. All meteorological and tracer concentration data have been edited and recorded on magnetic tape and are now available, upon request, at the National Computer Center, R.T.P., NC, either as copies or by interactive computer access.