Trigeminal primary afferents expressing P2X3 or transient receptor potential vanilloid 1 (TRPV1) are involved in the transmission of nociceptive information. In order to characterize P2X3- and TRPV1-immunopositive neurons in the trigeminal ganglion (TG) and trigeminal caudal nucleus (Vc), we performed immunofluorescence experiments using anti- P2X3 and anti-TRPV1 antisera and a morphometric analysis. 77.4% (1,401/1,801) of all the P2X3-postive neurons coexpressed TRPV1 and 51.9% (1,401/2,698) of all the TRPV1- immunopositive neurons also costained for P2X3 in the TG. Immunoreactivity for both P2X3 and TRPV1 were present in medium-sized neurons but not in small- and large-sized neurons. P2X3- and/or TRPV1-immunopositive fibers were observed in the primary afferents and their associated axons in the Vc. These fibers and terminals were distributed in the superficial lamina of Vc: P2X3-immunopositive fibers and terminals were distributed in the lamina I and II, expecially in the inner part of lamina II (lamina IIi), whereas TRPV1-immunopositive ones were densely detected in the lamina I and outer part of lamina II (lamina IIo). Immunopositive fibers and terminals for both P2X3 and TRPV1 were observed on the border between lamina IIi and IIo. These results suggest that terminals coexpressing P2X3 and TRPV1 are involved in specific roles in the transmission and processing of orofacial nociceptive information.