Inductive signaling mediated by secreted factors of the Hedgehog (Hh) gene family regulates cellular proliferation and differentiation in many embryonic tissues. Two transmembrane proteins associated in a complex, Patched (Ptc) and Smoothened (Smo), are indispensable for the reception of Hh signals (Cell 86 (1996) 221; Nature 382 (1996) 547; Nature 384 (1996) 176; Nature 384 (1996) 129). Here, we report on the identification of Ptc and Smo homologues from Xenopus and analyze their spatio-temporal expression during embryogenesis. The intracellular response to Hh signals involves upregulation of Ptc transcription (Genes Dev. 10 (1996) 301; J. Biol. Chem. 271 (1996) 12125). In accordance with its putative function as Shh target gene, XPtc1 expression during early stages of Xenopus embryogenesis is detected in mesodermal and neuroectodermal tissues proximal to the notochord, a known expression domain of Shh. Although the expression pattern of XPtc1 was similar to that of other vertebrates, expression domains specific to Xenopus could be detected in the hypochord, dorsal mesencephalon, otic vesicles and pituitary anlage. Unlike other vertebrate Ptc1 homologues, somitic expression of XPtc1 is confined to a central cell layer. In contrast to the tissue-specific expression characteristics of XPtc1, XSmo expression appears to be ubiquitously activated in early embryonic stages but condenses in the terminal regions of the embryo at tailbud stage. In many tissues and organs of the adult, XPtc1 and XSmo are found to display similar expression levels.