A 75-year-old woman was admitted with fever of unknown origin and liver damage, and treated with prednisolone. Hypercalcemia appeared when of the dose of prednisolone was reduced, and human T-cell lymphotropic virus type-I (HTLV-I) proviral DNA was detected in the leukemic cells by Southern blot analysis, and a diagnosis of acute adult T-cell lymphoma (ATL) was made. After chemotherapy with sobuzoxane was started, she went into septic shock caused by multiple resistant Serratia marcesense, and was treated with PMX-DHP and antibiotics. Although ner general condition and her serum cytokine leyels improved, the septic shock became more severe, and the patient died. Serratia marcesense expreses lipopolysaccharide (LPS), a biologically active substance that is present in gram-negative bacteria. Exposure to LPS leads to activation of cytokines, including TNF-alpha, IL-1beta, IL-6, and IFN-gamma. After treatment with PMX-DHP, the patient's general condition improved, but she died of septic shock. Bacterial infection may be a life-threatening complication in the immunocompromised hosts and elderly patients, particularly when granulocytopenia has been induced by chemotherapy, and thus such these patients require careful management.