Dear Editor, We report a patient of monoclonal gammopathy of undetermined significance (MGUS) with manifestation of pyoderma gangrenosum refractory to steroids and chemotherapy. Both the M-protein and pyoderma gangrenosum disappeared after autologous peripheral blood stem cell transplantation (PBSCT). A 33-year-old man suffered from rapidly enlarging pustular papules and plagues that ulcerated the necrotic base over his left leg 5 years ago (Fig. 1a). His serum immunoelectrophoresis revealed IgA-λ monoclonal gammopathy (IgA 782 mg/dL, normal 70–400 mg/dL; κ/λ 1.17, normal 1.35–2.69). Bone marrow examination disclosed slight plasmacytosis, which was less than 10% of all the nucleated cells (Fig. 1b). Without anemia (hemoglobin, 12.7 mg/dl; normal, 12–14 mg/dl), thrombocytopenia (platelet count, 426×10/l; normal, 150–430×10/l), osteolytic lesions, and impaired renal function, he was diagnosed as MGUS, IgA-λ, complicated with pyoderma gangrenosum. The patient was initially treated with methylprednisolone pulse therapy, but the response duration was short. He was then treated as having myeloma, but neither thalidomide nor chemotherapy with vincristine, Adriamycin, and Decadron regimen (VAD) was effective. High-dose cyclophosphamide (4 g/M) was given, and his peripheral blood hematopoietic stem cells were collected. Consequently, he received autologous PBSCT with 6.5×10/kg CD34+ cells infusion. Conditioning regimen included total body irradiation (6 Gy) and melphalan (140 mg/M). After the PBSCT, his skin has been free of lesions for 18 months (Fig. 1c). Serum immunoelectrophoresis could not detect the IgA-λ M-protein either. As a pre-malignant plasma cell proliferative disorder, MGUS has a lifelong risk of progression to multiple myeloma [1]. Different from those with myeloma, patients with MGUS have less than 10% plasma cells in bone marrow and do not require any treatment [2]. Various kinds of skin disorders have been associated with monoclonal gammopathy [3]. Some of these dermatologic disorders directly relate to the malignant plasma cells infiltration, but some are associated with the Mprotein. It is uncommon, however, that patients with MGUS manifest severe dermatologic diseases, especially pyoderma gangrenosum. A study from Mayo Clinic shows that nine of 86 patients with pyoderma gangrenosum had monoclonal gammopathy and seven had IgA [4]. Demitsu et al. report a patient of IgA MGUS-related neutrophilic, urticaria-like C.-M. Chang :W.-L. Hwang : C.-L. Teng (*) Division of Hematology/Oncology, Department of Medicine, Taichung Veterans General Hospital, 160, Section 3, Chungkang Road, Taichung 407( Taiwan, Republic of China e-mail: drteng@vghtc.gov.tw