The efficacy and safety of temozolomide were evaluated in 32 patients with anaplastic astrocytoma at first relapse. Temozolomide was administered orally once daily for the first five days of a 28-day cycle, at a dose of 150 or 200 mg/m(2)/day. The response rate determined by independent central review of MRI was 34% (95% confidence interval: 18.6%-53.2%), with 3 complete response and 8 partial response. The rate of "no change or better" was 91% (95% confidence interval: 75.0%-98.0%). Progression-free survival (PFS) at 6 months was 40.6%, and the median PFS was 4.1 months. The incidence of constipation (50%) and nausea (25%) was high,but these events were all mild or moderate in severity except in one subject with constipation,and could be managed with standard laxatives and antiemetics. The main laboratory test abnormalities (total incidence and incidence of grade 3/4 change) were lymphocytopenia (50%, 25%), neutropenia (47%, 6%), leukopenia (38%, 3%), thrombocytopenia (31%, 9%), and increased GPT (25%, 3%). Temozolomide was shown to have good efficacy and tolerability in patients with anaplastic astrocytoma at first relapse.