Parvalbumin- and calbindin D-28k-immunoreactivities (ir) were examined in the glossopharyngeal and vagal sensory ganglia (petrosal, nodose and jugular ganglia), the carotid sinus nerve and the carotid body. Parvalbumin-ir nerve cells were mostly localized in the petrosal and nodose ganglia and were rare in the jugular ganglion. Calbindin D-28k-ir nerve cells were found in moderate and large numbers in the petrosal and nodose ganglia, respectively. Only a few calbindin D-28k-ir nerve cells were observed in the jugular ganglion. The carotid sinus nerve and carotid body contained numerous calbindin D-28k-ir nerve fibers but few parvalbumin-ir nerve fibers. Studies of the coexistence of these calcium-binding proteins with calcitonin gene-related peptide (CGRP)- and tyrosine hydroxylase (TH)-ir showed that CGRP-ir was rarely colocalized in parvalbumin- or calbindin D-28k-ir nerve cells in the petrosal or nodose ganglion. Moreover, TH-ir was not generally contained in parvalbumin-ir nerve cells in the petrosal, nodose and jugular ganglia while a portion (15-19%) of calbindin D-28k-ir neurons in the petrosal and nodose ganglia colocalized TH-ir. These findings are consistent with the involvement of calcium-binding proteins, particularly calbindin D-28k, in the function of visceral sensory neural systems of the glossopharyngeal and vagus nerves and, perhaps, in baro- and chemoreceptor neurotransmission.