We have previously generated mice deficient for Nfe213 (NF-E2 p45 related factor 3 or Nrf3), a member of the cap 'n' collar family of basic-leucine zipper transcription factors. To examine whether Nrf3 is involved in chemical-induced carcinogenesis, we exposed the mice to benzo[a]pyrene (B[a]P), a carcinogen found in cigarette smoke. Contrary to wild-type mice, Nrf3-null animals are highly susceptible to B[a]P, exhibiting significantly increased mortality. Pathology analysis of affected tissue sections revealed a high incidence of T-cell lymphoblastic lymphoma in B[a]P-treated Nrf3(-/-) mice. Lymphoblastic lymphoma occasionally metastasized into the lung as demonstrated by perivascular malignant lymphocytic infiltration. Together, our studies show that the absence of Nrf3 predisposes mice to lymphoma development, suggesting a protective role of this transcription factor in hematopoietic malignancies. Our data demonstrate the first in vivo function of Nrf3 and its link to tumor development. Nrf3-deficient mice may serve as a preclinical mouse model to study carcinogen-induced lymphomagenesis.