This paper re-examines a previously published segmental map of the frog diencephalon (Puelles et al. [1996] Brain Behav.Evol. 47:279-310) by means of immunocytochemical mapping of calretinin, calbindin, and tyrosine hydroxylase. The distribution of neuronal populations, axon tracts, and neuropils immunoreactive for these markers was studied in adult specimens of Rana perezi and Xenopus laevis sectioned sagittally or horizontally. Emphasis was placed on study of the relationship of observed chemoarchitectural boundaries with the postulated overall prosomeric organization and the schema of nuclear subdivisions we reported previously, based on acetylcholinesterase histochemistry and Nissl pattern in Rana. The data reveal a large-scale correspondence with the segmental map in both species, although some differences were noted between Rana and Xenopus. Notably, retinorecipient neuropils were generally immunoreactive for calretinin only in Rana. Importantly, calretinin immunostaining underlines particularly well the transverse prosomeric boundaries of the dorsal thalamus. A number of nuclear subdivisions noted before with AChE were corroborated, and some novel subdivisions became apparent, particularly in the anterior nucleus of the dorsal thalamus and in the habenular complex. The mapping of tyrosine hydroxylase clarified the segmental distribution of the catecholaminergic cell groups in the frog forebrain, which is comparable to that observed in other vertebrates. Copyright 2000 Wiley-Liss, Inc.