Via NIH's Shared Instrumentation Grant Program, funds are requested to purchase a Cesium-137 irradiator designed for the whole body irradiation of mice. Major research applications are 1) Ablation of host bone marrow prior to transplantation; 2) Irradiation of antigen presenting cells in studies of T cell activation and development; and 3) Tests of ionizing radiation on the action of specifically mutated proto-oncogenes. This Cesium-137 irradiator would benefit a users group of 14 investigators in the following specific areas: B and T cell development and studies of TCR activation; macrophage mediated inflammation and wound healing; erythropoiesis and erythropoietin receptor signaling; and molecular mechanisms of proto-oncogene and viral oncogene action, including studies of Friend virus gp55, Sf-Stk, PPARb and Patched, and Piml.