A comparative assessment was made of dermatofibroma, dermatofibrosarcoma protuberans, and malignant fibrous histiocytoma. The study was comprised of an immunohistochemical investigation using the Ki-67 monoclonal antibody and a quantitative analysis of cell nuclear DNA using flow cytometry. It was found that the index of Ki-67 monoclonal antibody labeling, the histogram pattern, and DNA index correlated with clinical malignancy, suggesting the usefulness of these indices for differential diagnosis and evaluation of prognosis.