Clostridial collagenase has shown potential efficacy in vitro as an agent for clinical enzymatic fasciotomy for the nonoperative treatment of Dupuytren's disease, a fixed flexion contracture deformity of the hand caused by increased collagen deposition. In this study, the effects of clostridial collagenase (enzyme) injection into rat tail tendons were investigated in vivo for safety to assess potential adverse extravasation from the injection site to adjacent collagen containing structures. Results indicate that, at doses of 150 and 300 units purified clostridial collagenase, there was no adverse extravasation from the sacrocaudalis ventralis lateralis rat tail tendon injection site to adjacent tissue, including muscle, nerve, other tendons, vessels, bone, and skin. Clostridial collagenase appears safe as a nonoperative treatment for Dupuytren's disease but will require future clinical testing for efficacy.