Funds are requested to purchase a Gammacell-40 Exactor low dose research irradiator for use by scientists at the University of Texas at Austin and the University of Texas System Cancer Center, Science Park-Research Division, in Smithville, Texas. Current PHS-sponsored projects which will be served by the instrument involve: 1) studies of class I-specific CTL lines and T cell hybrids (Dr. Paul D. Gottlieb); 2) tumor suppressor genes in chemical carcinogenesis (Dr. Claudio J. Conti); 3) tumorigenicity of MMTV and studies of MMTV-encoded superantigen (Dr. Jaquelin P. Dudley); 4) effects of vitamin E on normal and retrovirally-suppressed immune responses (Dr. Kimberly Kline); 5) effects of lipids on interleukin-1 production (Dr. Mary F. Locniskar); 6) identity of the latent neoplastic epidermal cell (Dr. Rebecca J. Morris); 7) mechanisms of killing and cell signaling in cytotoxic T lymphocytes (Dr. Martin Poenie); and 8) identification of the target cell in MNU-induced lymphomagenesis and differentiation of murine thymoma cells after intrathymic transfer (Dr. Ellen R. Richie). The Phillips Norelco X-ray unit presently at the University of Texas at Austin, purchased in 1965, is unreliable, it is unsuitable for many of the projects proposed, and repair parts are not available. A 60Co irradiator fabricated by the Department of Nuclear Engineering in 1965 is cumbersome to use, its radiation source is substantially decayed, it is located thirty minutes from the campus, and it is presently not operative. No source of irradiation exists at the Science Park facility, and scientists there must make a four hour round trip by automobile to use a Gammacell-40 in San Antonio. Acquisition of a Gammacell-40 Exactor for use by scientists at the University of Texas at Austin and at Science Park will greatly facilitate research at both institutions.