Metabolism of 3H-tyrosine and 3H-dopaminc was studied with neuroblastoma cells in culture. This cell line (NB-I) was derived from a lesion metastatic to cervical lymph node obtained at autopsy from a 2.75-yr-old patient with neuroblastoma. l-Tyrosine hydroxylase activity in the culture cells was determined to be 167 pmoles dopa formed per mg protein per min. In the incubation medium with viable neuroblastoma cells, 3H-homovanillic acid was the major deaminated metabolite of 3H-tyrosine and of 3H-dopamine. Norepinephrine and its related metabolites were scarcely labeled in these studies. The findings obtained indicate that our neuroblastoma cell line is characteristic in that (i) contains a specific tyrosine hydroxylase activity and sufficient activities of catechol-O-methyltransferase, monoamine oxidase and aldehyde dehydrogenase, but (ii) probably lacks the activity of dopamine-β-hydroxylase.