A continuous cell line was established from an explanted tumor biopsy obtained from a patient with advanced neuroblastoma, which showed no response to chemotherapy. This cell line MHH-NB-11 retained most properties of the original immature tumor, even after xenotransplantation into nude mice. The cell line consisted of small dense cells with scant cytoplasm and thin; long processes and expressed neuron-specific enolase and synaptophysin, but neither GFAP nor S-100 protein. Karyotyping showed karyograms with 49 to 54 chromosomes, with a modal at 52. Most cells had trisomy 2,7,8,20, but only few structural aberrations were observed. Two of four chromosomes 1 showed a rearrangement of the terminal 1p segment, and all cells had a long HSR on the long arm of one of the chromosomes 13. This region hybridized in situ with the N-myc probe pNB-1. N-myc was amplified 20-fold in this neuroblastoma cell line as determined in Southern blot analysis. This cell line should be a useful tool in vitro or as a xenograft model for neuroblastoma research.