Matrix metalloproteinases (MMP) are involved in remodelling of the extracellular matrix (ECM) proteins suggesting that they play an important role in inflammatory process, in tumour invasion and metastasis. We examined immunohistochemically 330 cases of different skin disorders with the monoclonal antibody against MMP 11, stromelysin-3 (ST-3) protein. We found a positive immunoreactivity in fibroblasts surrounding malignant epithelial tumour cells in 63 of 125 cases (50.4%) of basal cell carcinomas, in four of 25 (16%) squamous cell carcinomas, whereas the tumour cells themselves were negative. Furthermore, the ST-3 protein could be detected in 23 of 40 cases (57.5%) of dermatofibroma, in two of five cases (40%) of atypical fibroxanthoma, in one of eight cases (12.5%) of dermatofibrosarcoma protuberans and, locally, in one of 10 cases (10%) of malignant fibrous histiocytoma. It was not present in the following skin lesions: keratoakanthomas (n = 12), Bowen's disease (n = 10), malignant melanoma (n = 12), melanocytic nevi (n = 28) and Kaposi's sarcomas (n = 25). In eczema (n = 10), psoriasis (n = 10) and virus-induced tissues (i.e. condylomata acuminata, n = 10) we did not observe an expression of ST-3 protein. We conclude first that ST-3 protein is a fibroblastic factor expressed in stromal cells adjacent to carcinoma cells; second, that ST-3 protein seems to be associated with benign fibroblastic tumours; and third, that it does not play a role in eczema, psoriasis or virus-induced skin lesions.