A glomangiosarcoma arose in a benign glomus tumour. The histological and immunohistochemical characteristics of the tumour were investigated. Apoptotic cells were identified by terminal deoxynucleotidyl transferase (TdT) mediated dUTP-biotin nick end labelling (TUNEL). The proportion of apoptotic cells was found to be low and TUNEL positive nuclei were present in the benign part of the tumour. Bcl-2 protein, an inhibitor of apoptosis, was strongly expressed in the glomangiosarcoma with only weak staining in the benign area. The proliferation index of the glomangiosarcoma was almost 10-fold higher than that of the benign glomus tumour. Numerous nuclei in the glomangiosarcoma were intensely stained for the tumour suppressor protein p53. The results of the this study may contribute to an understanding of the molecular basis of malignant transformation in benign glomus tumours.