We studied morphologic changes in olivary hypertrophy from dentato-olivary tract lesions by immunohistologic methods with antialpha B-crystallin and antiheat shock protein 27 (HSP 27). The majority of central chromatolysis-like enlarged neurons, which are frequently seen in the early stages of olivary hypertrophy on ipsilateral lesions, showed a marked expression of alpha B-crystallin; however, HSP 27 did not show increased expression in those neurons. In the later stages of olivary hypertrophy, increased expressions of alpha B-crystallin varied in the remaining neurons and the expression of HSP 27 increased in hypertrophied astrocytes, although the expression of alpha B-crystallin in hypertrophic astrocytes was not prominent. The accumulation of alpha B-crystallin and HSP 27 may represent responses to pathologic conditions.