The type III EGF receptor (EGFRvIII) is the result of an in-frame deletion from nucleotides 275 to 1075 in the EGF receptor cDNA sequence creating a novel epitope at the fusion junction. This spontaneously occurring alteration is found in a high percentage of primary human brain, breast, lung and ovarian tumors. We have explored whether a peptide derived from the fusion junction could serve as the basis for an antitumor vaccine. Preimmunization of mice with this peptide substantially inhibited tumor formation by cells expressing EGFRvIII. Tumor cell inoculation followed by immunization could also enhance the regression of existing tumors. Antibody production was elicited in animals that was highly specific for the novel epitope and also a CTL response that was mediated by CD8+ T lymphocytes. The alteration present in EGFRvIII could serve as the basis for an antitumor vaccine with potentially wide application in humans.