During tissue response to injury the glycoproteins fibronectin and Type III collagen are synthesized in increased amounts. We have studied the distribution of these molecules in the healing tendon at various times after injury by comparison with that of the major constituent of normal tendon, Type I collagen. Immunofluorescent localization demonstrated the presence of fibronectin throughout the tendon within one week after injury. Staining was found in the matrix, both around capillaries and around fibroblast-like cells. Fibronectin was still apparent in the healing tendon at one month after injury, but after a further two months was no longer detectable. Type III collagen was present both in pericellular and matrix locations until three months after injury, and matrix staining was apparent during the entire fourteen-month period under study. Type III collagen was also found throughout the matrix of the contralateral superficial flexor tendon during this period.