Although LIPUS has been shown to enhance fracture healing, the underlying mechanism of LIPUS remains to be fully elucidated. Here, to understand the molecular mechanism underlying cellular responses to LIPUS, we investigated gene expression profiles in mouse MC3T3-E1 preosteoblast cells using a GeneChip® system. The mouse preosteoblast MC3T3-E1 cells were treated with LIPUS (30 mW/cm2) for 20 min, followed by culturing for 24 h at 37?C. Mock-treated cells served as the control. Total RNA samples were prepared from the cells, and the quality of the RNA was analyzed using a Bioanalyzer 2100. Gene expression was monitored by an Affymetrix GeneChip® system with a Mouse Genome 430 2.0 array. Sample preparation for array hybridization was carried out as described in the manufacturer's instructions.