Cathepsins are lysosomal proteases that are distributed in many normal tissues and are primarily responsible for intracellular catabolism and turnover. The increased level of cathepsins in tumors together with their ability to degrade extracellular matrix proteins has led to the hypothesis that they are involved in the process of invasion and metastasis. We studied immunohistochemically the expression of cathepsins B, pro-D and pro-L in 8 cases of dermatofibrosarcoma protuberans (DFS), five cases of atypical fibroxanthoma (AFX) and twenty cases of dermatofibroma (DF). Expression of cathepsins B and pro-D could be detected in 5 of the 8 cases (62.5%) of DFS, whereas cathepsin pro-L was found in 4 (50%) cases. All AFX expressed cathepsin pro-L, whereas cathepsins B and pro-D were observed in 4 out of 5 cases. None of the malignant tumors showed a recurrence or metastasis after a period of four years. We found no expression of cathepsins in DF. In the epidermis and appendages, an expression of cathepsins pro-D, pro-L and B was seen. We conclude that cathepsins may be markers of increased metabolism rather than specific markers of malignancy.