Paraffin embedded tissues from twenty-two Thai patients with non-small cell lung cancer were studied for p53 gene mutations in exon 5 to 8 using polymerase chain reaction and single-stranded conformation polymorphism (PCR-SSCP) followed by thermal cycle sequencing. Results showed that point mutations in this region of p53 gene were present in 3 cases. One harboured the base change from GAC to AAC at codon 281, changing amino acid from aspartic acid to asparagine, whilst the other cases were transversion of AAA (lysine) to ACA (threonine) at codon 292. All subjects with p53 mutation had a past history of tobacco smoking.