A Phase I/II accelerated fractionation study for high-grade cerebral astrocytomas began in October 1987. Forty-two patients, 25 men and 17 women, were entered in the study. Median age was 58.5 years of age (range, 32 to 78 years). Performance status was 0, 1, 2, and 3 on Eastern Cooperative Oncology Group (ECOG) scale for 13, 19, 9, and 1 patients, respectively. Thirty-six patients had undergone partial resection, and six had stereotactic biopsy only. All patients had histologically proven astrocytomas (6 Grade 3, and 36 Grade 4). Treatment consisted of radiation therapy doses of 4400 cGy in 22 daily fractions to the whole brain plus a boost of 1600 cGy in 8 fractions given concomitantly with the last 8 whole-brain treatments using a twice daily schedule with an interfraction interval of 8 hours. Median survival time was 57 weeks from the date of starting irradiation. Survival was 50% and 28% at 1 and 2 years, respectively. Alopecia and scalp erythema were seen in all patients; nine patients had localized areas of moist desquamation in the retroauricular region. Decreased hearing and serous otitis media were seen in five patients within 1 to 2 months from the end of treatment. Increasing somnolence was marked in eight patients with progressive deterioration of performance status; computerized axial tomography (CAT) scan studies in all eight patients showed evidence of disease recurrence with associated brain edema and mass effect. Three patients had a second resection for a recurrent tumor with no evidence of brain necrosis at craniotomy. To date, the accelerated fractionation schedule appears to be well tolerated with valuable shortening of overall treatment time. The preliminary results are encouraging, and longer follow-up time is required to evaluate tumor control and toxicity.