Functional characteristics of the interstitial collagenase purified from the BCl rat mammary carcinoma cell line were examined and compared with literature reports of the corresponding characteristics of collagenase from non-neoplastic cells. BCl collagenase degraded soluble collagen types I, II and III at the same rate and degraded fibrillar tendon collagen with an activation energy of 75 kcal/mol; these characteristics were identical to collagenase from normal rat uterine smooth muscle cells. Degradation of fibrillar collagen by BCl collagenase was completely inhibited by rat alpha 2-macroglobulin which was concomitantly cleaved into half-fragments. BCl collagenase was also inhibited by native and recombinant tissue inhibitor of metalloproteinases, a synthetic peptide collagenase inhibitor (Z-pro-leugly-NHOH), and Zn2+. In all functional characteristics examined, BCl collagenase was the same as interstitial collagenases from non-neoplastic sources.