Evaluation of the radiation exposure data and the monitoring and recording procedures at each of the Oak Ridge plants is described in detail in our companion report . After reviewing these results we decided to limit our dose-response analysis to the sub-cohort of 28,770 white males who were ever employed at the X-10 or Y-12 plant (see Statistical Methods). About thirty percent of these workers were employed at more than one Oak Ridge facility. Most of the workers in the subcohort wore personnel monitoring devices that recorded estimates of their external dose over their employment history. For internal radiation exposure the monitoring policies and procedures varied considerably among facilities and over time [13,14]. In this combined analysis the internal radiation exposure was limited to variable to the three categories (see Materials and Methods and Table AIII).