A case-control study of brain tumor was conducted in collaborating hospitals in Boston, Providence, and Baltimore. Cases were 160 consecutive patients being treated for glioblastoma, grade 3 or 4 astrocytoma, or anaplastic astrocytoma. Controls were 128 healthy persons identified among the case's friends. A complex self-administered questionnaire was used to assess exposure to factors of interest. There was some evidence that glioblastoma is associated with a decreased susceptibility to allergies, a finding that may call attention to the involvement of immunologic disturbances in brain tumors. Our data are not supportive of previous reports of an association between brain tumors and exposure to pets or farm environment, family history of CNS malignancies or other neurologic conditions, or irradiation to the head. We did not find any evidence for an association with life-style characteristics such as cigarette smoking, alcohol consumption, use of drugs of any kind, or dietary intake of cured or smoked meat or fish.