We analysed 31 non-glioblastoma astrocytomas for alterations in p53 protein expression and for mutations in the p53 gene. Immunohistochemistry detected p53 protein accumulation in 71% (five of seven) of juvenile pilocytic astrocytomas (WHO grade I), 63% (five of eight) of astrocytomas (WHO grade II), and 63% (10 of 16) of anaplastic astrocytomas (WHO grade III). The single strand conformation polymorphism (SSCP) assay of exons 2-11 of the p53 gene and direct DNA sequencing identified p53 mutations in 14% (one of seven) of grade I, 25% (two of eight) of grade II, and 19% (three of 16) of grade III astrocytomas. This is the first report of a p53 mutation in grade I juvenile pilocytic astrocytomas. Immunohistochemistry and SSCP analyses gave concordant results in 55% (17 of the 31) of the tumors. A total of 14 tumors, 60-80% within each grade, showed p53 protein accumulation in the absence of detectable mutations of the p53 gene. No mdm-2 gene amplification was found in these tumors. The similar frequency of p53 alterations in tumors of grades I-III suggests that the p53 gene plays a significant role early in the formation of astrocytomas rather than late in tumor progression to higher grade. The data suggest that mechanisms other than p53 gene inactivation by mutation or mdm-2 complex formation result in the accumulation of P53 protein in > 70% of non-glioblastoma astrocytomas.