['To investigate biochemical changes in mouse tumour tissue following Microbeam Radiation Therapy (MRT) and Broad Beam (BB) irradiation using synchrotron Fourier-Transform Infrared (FTIR) microspectroscopy.', 'Synchrotron FTIR microspectroscopy was carried out on mouse tumour sections previously irradiated with BB (11, 22 or 44 Gy), MRT (560 Gy in-beam, 25 μm wide, 200 μm peak separation) or sham-irradiation (0 Gy) from mice culled 4 hours post-irradiation.', 'MRT and BB-irradiated tumour sections showed clear chemical shifts in spectral bands corresponding to functional group vibrations in protein (1654-1630 cm(-1)), lipid (~1470, 1463 cm(-1)) and nucleic acid (1130-1050 cm(-1)). MRT peak and valley regions showed virtually identical absorbance patterns in protein and lipid regions. However, we observed chemical shifts corresponding to the nucleic acid region (1120-1050 cm(-1)) between the peak and valley dose regions. Chemical maps produced from integrating absorbance bands of interest over the scanned tumour area did not reveal any microbeam paths.'] Does microbeam-irradiated tumour tissue possess a different infrared absorbance profile compared to broad beam and sham-irradiated tissue?