Factors regulating differentiation of the peripheral nervous system (PNS) have been widely studied in neuroblastomas which are tumors of the PNS. Five neuroblastomas were investigated for their content of tachykinin neuropeptides, which arise from two distinct genes which appear differentially expressed in the PNS. Radioimmunoassay and column chromatography revealed large amounts of neurokinin B in three of these tumors and the absence of substance P, neurokinin A, neuropeptide K and neuropeptide gamma from all five tumors. This suggests that neuroblastomas can selectively express the preprotachykinin (PPT) II gene and that they may be valuable for investigating the factors involved in the regulation of these two structurally-related neuropeptide genes.