We report here the discovery of Malassezia furfur from a groin abscess of a renal transplant patient. A 33-year-old male patient was admitted to our hospital because of a high fever and a persistent inflammatory nodule on his right groin for one week. He had received a renal transplant 3 years before and remained on immunosuppressive agents. He was treated with broad-spectrum antibiotics after hospitalization but the nodule formed a large abscess and then a deep ulcer instead of resolving. Examination of the culture by light microscopy revealed ovoid budding yeasts displaying collar-shaped structure. Subculture of the primary colonies onto Sabouraud's dextrose agar and medium containing rapeseed oil resulted in growth only on the medium containing rapeseed oil. All of the isolates was identified as Malassezia furfur. The pathogenicity of the isolates was tested in mice by intravenous injection of (3-5) x 10(8) cfu per mouse after immunosuppression with 500 mg/kg of prednisone intraporitoneally on day-2. In the mouse model, micro-abscess and inflammatory reaction and oval yeasts with budding were noted in histopathologic section of the viscera of the mice. A rib-like or serrate-like structure of the inner side of cell wall, characteristic for Malassezia spp., was observed by transmission electron microscopy. The patient received oral fluconazole and topical amphotericin B. The isolate before antifungal therapy was sensitive to both fluconazole and amphotericin B, while the isolate after antifungal treatment was only sensitive to amphotericin B. Proteinase activity of the isolates increased 1.43 times after antifungal treatment. This case indicated the invasive power of M. furfur in deep infection. Renal transplantation and reception of long-term immunosuppressive treatment are risk factors for the invasive infection of this fungus.