This study was performed to investigate the effect of ultrasound irradiation on $TGF-eta_1$ expression in the surgically injured achilles tendons of rats. The results of this study were as following: 1. The control group (3 days after injury) expressed little immunoreactivity for $TGF-eta_1$. 2. In the experimental groups, $TGF-eta_1$ immunoreactivity of group 11(applied US for 3 days) was increased markedly than that of group 1(applied US for 1 day). 3, The experimental group 11(applied US for 3 days) expressed higher immunoreactivity for $TGF-eta_1$ than control group. These findings suggest that ultrasound irradiation on the injured Achilles tendon may be of benefit such as increasing $TGF-eta$ release in the inflammatory phase of heal ins process.