Abstract The regional distribution of xenopsin-like immunoreactivity (XPLI) and of neurotensin-like immunoreactivity (NTLI) was studied by radioimmunoassay in tissues of Xenopus laevis and rat. In Xenopus laevis, XPLI showed a wide distribution throughout central and peripheral tissues with the highest concentration in the skin; NTLI was found in both central and peripheral tissues with the exception of the skin. Gel chromatography on Sephadex G-25 was used in order to characterize the immunoreactive material; both XPLI and NTLI eluted in a single peak at the position of synthetic xenopsin and neurotensin. No XPLI could be detected in central and peripheral tissues from mouse, rat, guinea-pig, rabbit or cat. In contrast, NTLI was found in a variety of peripheral tissues of the rat and it coeluted with synthetic neurotensin on reverse phase high-performance liquid chromatography. It is probably present in preganglionic parasympathetic nerve fibres.