Mutations of the p53 gene were investigated in 116 surgically removed primary brain tumor tissues by PCR-SSCP analysis. The mutations did not follow a random distribution among the various different subtypes, but occurred in 21.0% (13/62) of astrocytomas, 13.0% (3/23) of oligodendrogliomas and 35% (7/20) 35% (7/20) of PNETs. No mutation was found in the ependymomas. The majority of mutations identified in this study were G:C to A:T or C:G to T:A transitions (56.0%, 14 of 25) and occurred most frequently (56.0%, 14 of 25) at sites of CpG dinucleotides. Interestingly, codon 158 is a new hot spot which occurred with a frequency of 16.0% (4 of 25) in the samples analyzed.