Clarification of somatic mutations during the progression of human astrocytomas is important in order to understand the mechanisms underlying the development of these tumors. We analyzed surgical specimens of human astrocytomas for mutations in the p53 gene using single-strand conformation polymorphism analysis of polymerase chain reaction product (PCR-SSCP analysis) at a low pH. Klenow fragment treatment after PCR amplification was an effective means to get rid of some extra bands on the SSCP gel. Five mutations in three of 24 astrocytomas were identified by this improved SSCP method. The frequency of p53 gene mutations in astrocytomas examined was 12.5%. Further examination by direct sequencing showed that all five mutants had single-base substitutions resulting in missense mutations. The present studies revealed a loss of heterozygosity and two point mutations on the remaining allele in one of the fibrillary astrocytomas. Finally, the improvement of PCR-SSCP analysis using Klenow treatment and low pH showed a distinct electrophoresis gel pattern and could be relevant for the prognosis of human astrocytomas.