Healing of a partially ruptured gastrocnemius muscle was studied in rats with sonographical and histological techniques. Ultrasonography was performed 1-21 days after injury using a 7.5-MHz linear scanner. Following ultrasonography, the injured muscles were examined histologically. The injured area and development of hematoma were visualized during the first 5 days after trauma with ultrasonographical and histological observations. Later, disorganization of regenerating muscle fibers appeared sonographically more clearly than the scar tissue area demonstrated histologically. The present study points out the accuracy of ultrasonography in the examination of a muscle trauma, especially during the early phases of healing.