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Purpose: Effects of radiation sources used for total body irradiation (TBI) on Graft-versus-Host Disease (GvHD) induction were examined. Materials and methods: In a T cell receptor (TCR) transgenic mouse model, single fraction TBI was performed with different radiation devices (60Cobalt; 137Cesium; 6 MV linear accelerator), dose rates (0.85; 1.5; 2.9; 5 Gy/min) and total doses before allogeneic bone marrow transplantation (BMT). Recipients were observed for 120 days. Different tissues were examined histologically. Results: Acute GvHD was induced by a dose rate of 0.85 Gy/min (60Cobalt) and a total dose of 9 Gy and injection of 5×105 lymph node cells plus 5×106 bone marrow cells. Similar results were obtained using 6 MV linear accelerator- (linac-) photons with a dose rate of 1.5 Gy/min and 0.85 Gy/min, a total dose of 9.5 Gy and injection of same cell numbers. TBI with 137Cesium (dose rate: 2.5 Gy/min) did not lead reproducibly to lethal acute GvHD. Conclusions: Experimental TBI in murine models may induce different immunological responses, depending on total energy, total single dose and dose rate. GvHD might also be induced by TBI with low dose rates. [ABSTRACT FROM AUTHOR]