Neurotensin is a tridecapeptide with changing receptor expression in central and peripheral neural cells during ontogeny suggesting its potential use as a differentiation and tumor marker in neuroectodermal malignancies. We investigated the neurotensin levels in plasma samples of 58 patients with neuroblastoma using a sensitive radioimmunoassay. Elevated levels were found only in one stage III and in one stage IVs patient, while the neurotensin concentrations of 56 patients were in the range of control children. We conclude that plasma neurotensin reflects neither the differentiation nor the tumor status in children with neuroblastoma.