Mouse YC8 T cell lymphoma was used as a model to determine whether an effective immunotherapy procedure could be devised for the treatment of lymphoma localized to the brain. Implantation of 5 x 104 YC8 cells into the left cerebral hemisphere induced rapid loss of the animal's body weight. Severe loss of weight and early deaths were observed in the untreated control group. Although resistance can be conferred to the brain by immunization of naive BALB/c mice, adoptive chemoimmunotherapy procedures were surprisingly not effective in inducing remissions in animals with lymphoma confined to the brain. Even passive transfer of effector cells from immunized, tumor resistant donor animals combined with systemic IL-2 treatment did not impart resistance to recipients with brain tumors. However, regression of the intracranial tumor and apparent cures could be accomplished, when ex vivo cultured effector cells were transferred intravenously.