Fibroblast cultures derived from human basal cell carcinomas demonstrated an increased capacity to synthesize and secrete collagenase. Although the levels of collagenase were up to 8-fold greater than those of normal control cell lines, this phenotypic trait was not permanent and was expressed only for a few passages following primary explanation. The basal cell carcinoma fibroblast collagenase was secreted as a proenzyme. The kinetics of activation and the catalytic efficiency of the basal cell carcinoma fibroblast enzyme were equal to control collagenase, indicating that increased activity was due to increased synthesis of enzyme protein. Increased synthesis of collagenase was not due either to altered cell growth or to an overall increase in protein synthesis. Furthermore, synthesis of another major protein, of another major protein, collagen, was not enhanced. The data suggest that the tumors may have stimulated adjacent fibroblasts to produce more collagenase which is of importance in tumor invasion.