Sonography has been widely applied to the examination of human muscles in both static and dynamic conditions. Many studies were also reported on the sonographic assessment of muscles and nerves of human and hand. To the authors's knowledge, no study has been reported on the relationship between the dimensional changes of muscles obtained by sonography and the corresponding joint angles. In this paper the dynamic ultrasound image of muscle and the derived dynamic signals, termed sonomyography (SMG). is introduced, and a preliminary analysis of SMG sampled from forearms during wrist flexion-extension is made based on image processing. Potential applications of SMG are mentioned. ; Department of Health Technology and Informatics