Direct associations between serum concentrations and immunohistochemically detectable vasoactive intestinal peptide (VIP) and maturing neuroblastoma have been documented. Furthermore, VIP has been shown to induce both the growth inhibition and morphological differentiation of cultured human neuroblastoma cell lines. As such, it is hypothesized that VIP may be operative in the autocrine regulation of neuroblastic growth and differentiation. To test this hypothesis, VIP-induced differentiation of human neuroblastoma LA-N-5 cells was performed. Significant concomitant increases in both intracellular and extracellular VIP concentrations were observed. In addition, a marked increase in VIP receptor expression was demonstrated with VIP-induced cellular differentiation. Receptor function was maintained with enhanced expression, as evidenced by an increase in the generation of intracellular cyclic adenosine monophosphate in response to exogenous VIP stimulation. Concomitant enhancement of both intracellular and extracellular VIP expression, coupled with the induction of functional specific VIP receptors during VIP-induced differentiation, provides critical evidence for the autocrine regulation of neuroblastoma maturation by this peptide.