Short-term effects of application of histamine to the nasal mucosa on trigeminal ganglion neurons containing calcitonin gene-related peptide (CGRP) and substance P (SP) were examined in guinea pig. Immunoreactivities to CGRP and SP in these neurons were decreased 30 min after the histamine application. The decreases were most marked at 1-3 h after application, after which the immunoreactivities began to increase, reaching the base line by 6 h after the application. The immunoreactivities to CGRP and SP in the nerve endings of nasal mucosa were not decreased. The expression of mRNAs for both peptides in the soma of trigeminal neurons was unchanged. The histamine application to the nasal mucosa may cause release of CGRP and SP from terminals of peripheral processes of trigeminal ganglion neurons, and enhance axonal transport of these peptides, but does not affect their biosynthesis in the soma of trigeminal ganglion neurons.