Non-suppurative encephalitis was experimentally induced in three-week-old piglets by a single intranasal inoculation of Japanese encephalitis virus (JEV) isolated from field pigs. The lesions consisted of glial cell aggregates and perivascular cuffing throughout the olfactory tract and pyriform cortex. JEV antigens were detected in the cytoplasm and neuronal processes of small nerve cells in the granule cell layer of the olfactory bulb, in the neuronal processes of the olfactory tract and in the cytoplasm of neurons in the pyriform cortex. The distribution of the antigens corresponded closely with the distribution of brain lesions. These findings suggest that JEV may enter the brain by the olfactory pathway in addition to via haematogenous spread in piglets.