AbstractThis paper is concerned with the evaluation of thein vivoperformance characteristics of reconstituted bovine collagen as an insoluble carrier matrix for therapeutic enzymes. The enzyme that was chosen as a model for this evaluation wasE. coliL‐asparaginase, which has been widely investigated as a soluble chemotherapeutic agent for the treatment of acute lymphocytic leukemia in humans (Oettgen et al.,Cancer Res.,27, 2619, 1967; Beard et al.,Brit. Med. J.,1, 191, 1970; Ohnuma et al.,Cancer Res.,30, 2297, 1970). The results presented here were obtained from perfusion trials with a collagen–asparaginase reactor incorporated into an extracorporeal circuit attached to the vascular systems of healthy mongrel dogs. A series of 1–2 hr perfusions were conducted with a single collagen‐asparaginase membrane over a period of 4 months. Serum asparagine levels were reduced by more than 98% after 15–30 min perfusion time. Red blood cell (RBC), hemoglobin, hematocrit, and fibrinogen values remained constant during each perfusion. An average decrease of 48% in white blood cell (WBC) and 24% in platelet levels was observed, but these values began to rise slowly even before cessation of the perfusion. No serious toxic or antigenic reactions or mechanical or clotting difficulties were observed.In vitroactivity, when assayed between perfusions, remained constant over a period of 4 months of intermittent use and storage. The potential advantages of collagen–enzyme complexes for the administration of therapeutic enzymes i