A cDNA, which has a high homology with teleost Platichthys flesus [Arg8] vasotocin (AVT) receptor (GenBank: AK033957), was found in mouse genome database. Analyses of the deduced amino acid sequence revealed that a cDNA has several features of AVT receptor. We tentatively named it as a mouse vasotocin receptor (MVTR). A two-electrodes voltage clamp technique was applied to characterize the MVTR expressed in Xenopus laevis oocytes. AVT induced Ca2+-dependent Cl- currents in Xenopus oocytes injected with MVTR cRNA. On the other hand, [Arg8] vasopressin, oxytocin and isotocin did not induce such currents. RT-PCR showed that MVTR mRNA was specifically expressed in the brain. In situ hybridization analysis demonstrated significant expression of MVTR mRNA in suprachiasmatic nucleus, arcuate nucleus and medial habenular nucleus of mouse brain. These results suggest that MVTR may mediate a variety of physiological functions in mouse.