Healing canine flexor tendons were treated with early controlled passive mobilization. The repair site and proximal and distal tendon stumps were stained for fibronectin and examined by light microscopy at three, seven, eleven, and seventeen days. Fibronectin increased dramatically in the epitenon adjacent to the repair site seven days after repair, a time when epitenon cellular activity was at its peak. By seventeen days, fibronectin staining had decreased substantially, both at the repair site and in the tendon stumps. A delayed increase in fibronectin activity was noted in the endotenon adjacent to the repair site. Fibronectin production appears to be an important component of the early tendon repair process. Fibroblast chemotaxis and adherence to the substratum in the days after injury and repair appears to be related directly to fibronectin secretion. This study is the first to provide documentation of fibronectin localization in a clinically relevant tendon repair model.