Abstract: BALB/c mice which had developed protective immunity against Plasmodium yoelii (P.y.) challenge were injected with anti-CD4 or anti-CD8 monoclonal antibody,and were then challenged again with P.yoelii.No impairment of protection was observed.CD8+T cells obtained from spleens of these mice were transferred to BALB/c nude mice and induced partial protection,while transfer of CD4+T cells did not so.In P.yoelli-mouse model,the parasites invaded reticulocytes in the early infection,and the infected reticulocytes could be recognized and attacked by sensitized CD8+T cells.In late infection when P.yoelii also invaded mature erythrocytes,the protective effect of CD8+T cells decreased and the main role of protection was played by antibodies.