In neuroblastic tumors a relationship of differentiation of the tumor to galanin receptor expression and antiproliferative and apoptotic effects upon activation of galanin receptors in neuroblastoma cells was reported. To elucidate the expression of other components of the galanin peptide family in neuroblastic tumors, RT-PCR analysis of a variety of human neuroblastic tumor tissues was performed. Ganglioneuroma tissues revealed the presence of a splice variant of the galanin-like peptide (GALP) mRNA, which results in exclusion of exon 3 and a frame shift after the signal peptide sequence of GALP. This generates a peptide of 25 amino acids, which we have termed alarin because of the N-terminal alanine and the C-terminal serine. The novel neuropeptide alarin does not reveal significant homology to other peptides. Immunohistochemistry with antibodies directed against synthetic alarin peptide detected specific cytoplasmic granular staining in ganglia of human ganglioneuroma and ganglioneuroblastoma, as well as differentiated tumor cells of neuroblastoma tissues. Undifferentiated neuroblasts of these tumor tissues did not show alarin-like immunoreactivity and alarin-specific mRNA. Our findings indicate that alarin expression is a feature of ganglionic differentiation in neuroblastic tumor tissues.