Augmented soft tissue mobilization therapy (ASTM) is a newly developed massage technique. ASTM is applied with the aid of specifically designed, solid instruments and has been successfully used in the treatment of chronic tendinitis patients. In a study on collage nase -injure d rat Achilles tendons treated with ASTM, Davidson et. al (1997) reported gait improvement as well as fibroblasts proliferation and suggested ASTM may augment healing by the recruitment of fibroblast. The present study examined the morphological response of enzyme-induced rat Achilles tendons to 3 different ASTM pressure application: 1 newton; 2 newtons and 3 newtons. Collagenase-injured tendons exhibited disrupted and randomly arranged collagen fibers. Treatment applications were performed for 4 days for a total of 4 treatments. Morphological differences were demonstrated between groups in proportion to the ASTM treatment pressure application. The ASTM group treated with 3 newtons demonstrated the greatest mean fibroblast count (370.3 +/- 51.6). Further, electron microscopy revealed the presence of activated fibroblasts in the tendons of the 3 newtons, ASTM group. However, immunochemical staining comparisons of Type I and III collagen, fibroblast growth factor receptor, and insulin-like growth factor between groups were not remarkable. / Department of Physiology and Health Science