['Procarbazine usage in brain tumors has a high incidence of hypersensitivity reactions compared with its use in other malignancies. Procarbazine oxidation to a reactive intermediate is enhanced by phenobarbital. Patients with primary brain tumors would have a preferential exposure to anticonvulsants compared to patients with other malignancies.', 'To determine whether anticonvulsant exposure is associated with procarbazine hypersensitivity reactions in patients with primary brain tumors.', 'This retrospective cohort study included 83 patients with primary brain tumors who were treated with procarbazine between 1981 and 1996 at a university hospital-based regional oncology center. Data were extracted by chart review. The data collected included age, sex, race, tumor type, smoking, alcohol usage, and all concomitant medications, as well as creatinine, aspartate aminotransferase, total bilirubin, and anticonvulsant serum levels. Anticonvulsant exposure was determined by the presence of detectable serum levels. Cases of procarbazine hypersensitivity reactions were identified through a review of progress notes.', 'There were 20 patients with procarbazine hypersensitivity reactions. A significant association between the exposure to anticonvulsants and the development of procarbazine hypersensitivity reactions was found (p = 0.05). In addition, there was a significant dose-response association between the development of procarbazine hypersensitivity and the presence of therapeutic anticonvulsant serum levels (p = 0.03).'] Is anticonvulsant usage associated with an increased risk of procarbazine hypersensitivity reactions in patients with brain tumors?