It is the aim of the proposed research to compare and contrast the radiobiological properties of the non-tumorigenic and tumorigenic forms of otherwise well characterized human hybrid cell lines (HeLa x human skin fibroblasts). Since the transformation from non-tumorigenic to tumorigenic forms is associated with certain well-defined changes (e.g. loss of specfic chromosomes) these cell lines offer a unique system with which to study the genetic control of radiosensitivity. In addition radiobiological studies may indicate oher changes in cellular properties which accompany malignant transformation (e.g. reduction in DNA repair capability). Furthermore our preliminary studies indicate that these human hybrid cells significant potential for the study of radiaton-induced ongocenic cell transformation. It is therefore an additional aim of this proposal to develop a methodology for the quantitative study of radiation-induced oncogenic cell transformation using hybrid human cells. A proposed methodology for this involves detection of malignantly transformed cells using an monoclonal antibody for a tumor-specific membrane protein and flourescence activated cell sorting.