A method utilizing the enzyme-linked immunosorbent assay (ELISA) is presented for quantitating fibronectin in periarticular soft tissues from rabbits. The concentrations of fibronectin were determined in the medial collateral ligament, anterior cruciate ligament, posterior cruciate ligament, and patellar tendon. The anterior cruciate and posterior cruciate ligaments, surrounded by a synovial sheath, had similar amounts of fibronectin that were each over twice as high as that found in either medial collateral ligament or patellar tendon which have no sheath covering.