Histological, immunohistochemical, and ultrastructural studies were performed on two cases of histologically unusual extramammary Paget's disease. Histologically, the central area of the lesions showed a bowenoid pattern, and the peripheral area showed typical extramammary Paget's disease. The transition zone showed an intermediate pattern. All these areas were positive for CEA and EMA, and negative for S-100 protein. Ultrastructurally, in the intermediate pattern, the tumour cells had abundant cytoplasmic glycogen, and the widened intercellular spaces contained numerous glycogen particles, which were probably secreted by the tumour cells. It is well known that eccrine glands, but not apocrine glands, secrete glycogen particles. Therefore, the present findings suggest that some cases of extramammary Paget's disease are a proliferation of germinative cells with eccrine gland differentiation.