The aim of our research is to clarify the mechanisms generating heterogeneity in response to C-ion irradiation that arise from individual genetic variations in humans. In this study we performed whole lung C-ion irradiation using three different strains of mice to examine whether strain-dependent differences in radiation effects occur in high-LET C-ion thoracic irradiation. Murine strain-variance was evaluated by histopathological examination of intra-alveolar hemorrhage that is likely to occur during the early phase after irradiation and of lung fibrosis during the late phase occurring more than three months after irradiation. We also performed microarray analysis to identify the key genes that are differentially regulated in different mouse strains after C-ion irradiation and to determine the mechanism of strain-dependent pulmonary damage after high-LET C-ion irradiation. Eight-week old female inbred C3H/He Slc C57BL/6J Jms Slc and A/J Jms Slc mice (3 kinds of mice) were used. The whole thorax of three mice was locally irradiated at 10 Gy with C-ion beams with a reference beam 137Cs gamma-rays (2 kinds of beam). Three mice of each strain (3 mice) were sacrificed and immediately dissected for lung extraction at 6 h (6h sample). Lungs for three mice of each strain without irradiation were extracted at the same time as control samples (control sample). Hybridization to microarrays (Whole Mouse Genome 4x44K OligoMicroarray Kit single color Cyamine 3-CTP) consisting of 44,000 total spots was conducted using an Agilent Gene Expression hybridization kit. The arrays from three independent replicates for each sample (3 arrays) were scanned on an Agilent dual-laser Microarray Scanner (all from Agilent Technologies) following the manufacturer s instructions. A total of 108 samples were analyzed. 3 replicate arrays x 3 mice x 3 strains x 2 timing for sampling x 2 kinds of beam.