Since Bcl-2 protects a variety of cell types from programmed cell death, whereas Bax promotes apoptosis, the present study examines Bcl-2 and Bax proteins, and bcl-2 and bax mRNA expression in the developing cerebellum of the rat following methylazoxymethanol (MAM) acetate administration by using immunohistochemistry, Western blotting and Northern blotting. Bcl-2 expression in the developing cerebellum is observed in proliferating and differentiating cells, whereas Bax expression is higher in differentiating cells than in proliferating cells during development. Administration of MAM (0.05 microliter/g, i.p.) at postnatal day 3 produces apoptotic cell death, as detected by the characteristic morphology and positivity with the method of in situ end-labeling of nuclear DNA fragmentation of dying cells, in the external granule cell layer of the cerebellum. Dying cells are not stained with Bcl-2 and Bax antibodies. Furthermore, no modification in the intensity of Bcl-2 and Bax protein bands and in the intensity of Bcl-2 and bax mRNA bands on Western and Northern blots, respectively, were observed between control and treated rats. These data indicate that MAM-induced apoptosis is not associated with modifications in the expression of Bcl-2 and Bax.