Abnormal p53 as revealed by immunostaining has been shown to be a predictor of poor outcome in a variety of malignant tumors. This study examines the relationship of p53 immunostaining and survival in 182 adult patients with gliomas. Tumor tissues obtained from patients with glioma within 4 months of initial diagnosis were investigated by immunohistochemical analysis for detection of p53 protein abnormalities using the monoclonal antibody PAb 1801. There were 122 patients with glioblastoma multiforme, 48 patients with anaplastic glioma, and 12 patients with low-grade glioma. Among these patients, 73 of those with glioblastoma multiforme, 35 with anaplastic glioma, and 6 with low-grade glioma had positive p53 immunoreactivity. Kaplan-Meier survival plots (log rank test) showed that the patients with anaplastic astrocytoma or low-grade glioma and p53-positive tumors had longer survival times compared to the patients with p53-negative tumors. No differences in survival were detected among the glioblastoma patients. Cox proportional hazards regression analysis, adjusted for age at diagnosis, showed that the p53 positivity was a significant predictor of longer survival (relative risk = 0.56; 95% confidence intervals = 0.35, 0.90; P = 0. 015) in anaplastic astrocytoma patients, but not in glioblastoma patients (relative risk = 1.03; 95% confidence intervals = 0.82, 1. 29; P = 0.80). These results suggest that anaplastic glioma patients with p53 protein alterations may have a better response to chemoradiation, possibly because the malignant cells cannot arrest in G1 to correct lethal damage induced by chemotherapy or radiotherapy.