A peculiar human cell line (GI-ME-N) derived from the metastatic bone marrow of a 2-yr-old patient with stage IV neuroblastoma (NB) was extensively characterized. Cell-type-specific markers, tumorigenicity in nude mice, morphology, cytogenetics, and amplification/expression of the N-myc gene were evaluated. All metaphases presented the typical 1p deletion. Surface markers specific for NB cells, vimentin, and neurofilament proteins were all clearly detectable with immunofluorescence and/or western blot procedures. Moreover, it was found that GI-ME-N cells did not express N-myc oncogene or HLA class 1 antigens, and were not classified as peripheral neuroectodermal tumor cells. However, extremely short latency and survival times, comparable to peripheral neuroectodermal tumor cells, were observed in nude mice grafted with GI-ME-N. In addition, no correlations were. observed in tumorigenicity of N-myc amplified (IMR32)versusunamplified (SK-N-SH GI-ME-N) human NB cell lines in nude mice. We conclude that N-myc amplification/ expression do not correlate with the aggressiveness of human NB in athymic animals, which is not always explained by the peripheral neuroectodermal tumor cell nature of the malignant cells, either.