Forced circulation during and after the Three Mile Island Unit 2 accident distributed reactor fuel into the systems and components of the reactor building (RB) and the auxiliary/fuel handling building (AFHB). Most of the fuel remained in the reactor coolant system and the RB, with smaller amounts continuing to the AFHB systems. Efforts began in 1985 to determine the location and amounts of ex-vessel fuel debris. An overview of the fuel characterization measurements in the RB external to the reactor vessel is presented. The fuel characterization was performed using six methods: neutron assay, alpha assay, sampling, visual inspection, gamma spectrometry, and gross gamma radiation measurements. The method used for the best estimate for a particular region depended largely on the environment and often employed a combination of methods. Using these methods, the minimum and maximum amounts offuel were estimated for each ex-vessel location in the RB. Estimates indicate that between 76.2 and 215.1 kg of reactor fuel currently remain in the RB ex-vessel areas.