Stage IVs neuroblastoma is a unique cancer that shows spontaneous regression, although it does exhibit metastasis to the spleen or liver [1]. The mechanisms of spontaneous regression of the tumor are not precisely known, but endogenously programmed biological mechanisms such as apoptosis are suspected [2]. In addition, immunologic mechanisms such as cell-mediated immunity have also been speculated [3]. Granulysin is a recently defined cytolytic granule protein of natural killer cells and cytotoxic T-lymphocytes [4,5]. It has been demonstrated to possess antimicrobial effects when used in isolation against a variety of pathogens, including bacteria, fungi, and parasites [6-8]. Furthermore, granulysin is believed to contribute to antitumor and antiviral immune responses through its tumoricidal and antiviral activities [9]. Recently, we have established an enzymelinked immunosorbent assay system that detects granulysin in the serum [5]. We treated a girl with stage IVs neuroblastoma; during the spontaneous regression of the tumor, her serum granulysin level was markedly increased. A 2-month-old girl was admitted to our hospital because of an abdominal tumor. She had been admitted to a hospital at 1 month of age because of bronchiolitis from a respiratory syncytial virus infection; hepatomegaly was not noted at that time. The parents noticed distention in the patient’s abdomen, which was progressing day by day 1 week before admission. A computed tomography scan showed a markedly enlarged liver, which extended to the pelvic cavity. A systemic bone survey revealed no abnormal findings. Magnetic resonance imaging showed heterogeneous multifocal masses occupying the liver, but the primary site could not be determined. Scintigraphy testing (metaiodobenzylguanidine I 123) disclosed no metastatic site other than the liver. Bone marrow aspirated from the right tibial bone showed no invaTransient Increase of Serum Granulysin in a Stage IVs Neuroblastoma Patient during Spontaneous Regression: Case Report