Tumor-selective surface antigens may be targets for diagnosis and immune-based therapies. Monoclonal antibody 8H9 is a murine IgG1 hybridoma derived from the fusion of SP2/0 mouse myeloma cells and lymphocytes from BALB/c mice immunized with human neuroblastoma (NB). 8H9 reacts with a surface antigen on NB cell lines NMB7 and LAN1 by immunofluorescence. By immunohistochemistry, it is nonreactive with normal human tissues, including bone marrow, colon, stomach, heart, lung, muscle, thyroid, testes, pancreas, kidney and brain (frontal lobe, cerebellum, pons and spinal cord), but moderately reactive with human hepatocytes. Reactivity with normal tissues from cynomolgus monkey was similarly restricted. 8H9 is reactive with human brain tumors, childhood sarcomas, NB and less so with adenocarcinomas. Among brain tumors, 14/18 glioblastomas, 3/6 high-grade gliomas, 3/3 astrocytomas, 3/6 oligodendrogliomas, 2/3 meningiomas, 1/1 of medulloblastoma and 1/1 schwannoma. Among sarcomas, 12/12 Ewing's/PNET, 8/8 rhabdomyosarcomas, and 6/7 osteosarcomas also tested positive with 8H9. 20/26 NB and 8/16 adenocarcinomas(2 metastatic to the brain) were positive. 8H9 could be purified by protein-G affinity chromatography and radiolabeled with 99mTc via hydrazino nicotinamide derivative; human NB xenografts in nude mice showed selective tumor uptake. When injected intravenously with 99mTc-8H9, normal cynomolgus monkey demonstrated uptake in the liver as well as ends of long bones. This tumor-selective antigen expressed on a broad range of pediatric and adult cancers may have clinical utility in diagnosis and therapy. Further biochemical characterization is warranted.