To explore the regulatory mechanism of the release of neuropeptides in nasal mucosa, the distributions of somatostatin (SOM) and SOMmRNA-immunoreactivities (IR) in cryostat sections of rat nasal mucosa and trigeminal ganglion (TG) cells were investigated using immunohistochemistry (ABC technique) and in situ hybridization histochemistry. The recombinant PSP65 plasmid (400 SOMcDNA) in vitro worked as a plate for the preparation of SOMmRNA single strand (cRNA) probe, which was labelled with digoxigenin. The results showed that neither of these two substances reacted positively in nasal mucosa but positive SOM-IR and SOMmRNA-IR signals were definitely seen in TG cells. In contrast with SOM immunohistochemistry, SOMmRNA-IR positive granules tended to be located in the cytoplasm of TG cells, with a clearer background and a higher resolution rate. The significance of SOMmRNA in TG cells was briefly discussed. It was concluded that SOMmRNA in TG cells might be involved in the regulation of the release of neuropeptides in nasal mucosa.