Neuroblastoma cell lines have been reported to contain two proopiomelanocortin (POMC) mRNA transcripts. We have now shown by immunocytochemistry and radioimmunoassay (RIA) that a number of neuroectodermally derived cell lines contain immunoreactive beta-endorphin although cell concentrations were not characteristic of any tumour type. To explore further the functional significance of beta-endorphin expression, we analysed neuroblastoma cell lines having intermediate (I), substrate adherent (S) and neuronal (N) phenotypes. No differences in cell beta-endorphin content were detected. However, the expression of POMC mRNA and of immunoreactive beta-endorphin was reduced within a few hours of treatment of these cell lines with retinoic acid. Culture of the cell lines in the presence of beta-endorphin resulted in small but significant increases in growth. Although the POMC gene is in the same chromosomal segment as N-myc, which is normally amplified in neuroblastoma, no corresponding amplification of POMC could be demonstrated. The data suggest that POMC gene products may contribute to the autocrine/paracrine growth of neuroectodermal tumours.