Detection of catecholamine production by neuroblastoma is a useful tumor marker. The majority of neuroblastoma patients have elevated levels of urinary catecholamines and/or their metabolites, and have tumors, which show histochemical evidence of catecholamines using glyoxylic acid-induced catecholamine fluorescence. By contrast, continuous cell lines derived from neuroblastomas lack catecholamine fluorescence in vitro. In this study, we report that 11 out of 12 human neuroblastoma cell lines established from catecholamine-positive tumors displayed histochemical evidence of catecholamines when grown as xenografts in athymic (nude) mice. Catecholamine fluorescence in these xenograft tumors decayed over a 5 day period when the cells were placed into tissue culture. Xenograft tumors of cell lines derived from four catecholamine-negative neuroblastomas or seven primitive neuroectodermal tumors (PNET) did not show catecholamine fluorescence. Ultrastructural comparisons of cell lines in vitro with their corresponding tumors in vivo showed that six of eight cell lines had fewer dense core (neurosecretory) granules in vitro compared to the more readily detectable dense core granules seen in nude mouse tumor tissue. These data indicate that catecholamine synthesis and/or storage in human neuroblastoma cells requires factor(s) not present in the in vivo environment. As neuroblastoma cell lines derived from catecholamine-positive tumors retain the ability to produce and store catecholamines in vivo, such cell lines can be used to identify factors critical to catecholamine production in human neurons.