Procarbazine is effective in the treatment of malignant gliomas. We retrospectively reviewed all glioma patients treated with procarbazine at a dose of 150 mg/m2 daily for 28 days, every eight weeks, to determine incidence and prognostic factors associated with the development of Herpes Zoster. Ten of sixty-four (16%) patients developed Herpes Zoster infections; this group was found to have received a greater number of courses of procarbazine (5.1+/-1.2 v. 1.6+/-.2, p<.001) and have significantly less neutropenia when compared to the group receiving procarbazine who did not develop the infection. Infection developed at a median of 4.1+/-1.1 courses. Herpes Zoster infection is common in brain tumor patients taking procarbazine, and is associated with multiple drug courses and a normal WBC count. Immune function studies that could identify patients at high risk for Herpes Zoster might lead to the prophylactic use of acyclovir.