The Environmental Protection Agency's (EPA's) Radon Mitigation Branch (RMB) conducts research and development on the reduction of indoor radon levels. Finding that there was no comprehensive database on the physical characteristics of the nations's school buildings (with information specific to radon-mitigation research), the RMB conducted a study that measured radon levels in a subsample of 100 schools from the Environmental Protection Agency's (EPA's) National School Radon Survey (NSRS). The schools were visited to obtain information on building structure and age, location of utility lines, and the type of heating, ventilating, and air-conditioning (HVAC) system. Building-characteristic profile sheets for all schools were then compiled. Information from each school was entered into a database to determine the relative proportions of physical characteristics of America's school-building population. This paper describes the sample-selection process, preliminary findings from the profile sheets, and the statistical limitations of the study. The results will be used by the EPA to guide further radon-mitigation research in schools. The building characteristics will also be correlated with school radon levels to identify any relationships between the physical characteristics and radon levels. Six figures and five tables are included. (LMI)