The frequency distribution of four cytochrome P4501A1 (CYP1A1) gene mutations was investigated in 271 Turks from southeast Anatolia by polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) assay. Allelic linkage of those mutations was proven by peptide nucleic acid-mediated PCR clamping. Mutation ml (T6235C) forming an MspI restriction site in the 3'-flanking region occurred with 18.1% frequency (95% confidence interval 14.9-21.6%), m2 (A4889G) leading to an Ile/Val exchange in exon 7 had a frequency of 8.9% (6.6-11.6%), and m4 (C4887A; Thr/Asn-exchange also in exon 7) occurred with 5.7% (3.9-8.0%). T5639C (m3) in the 3'-flanking region was not detected. m2 was exclusively found linked with ml forming allele CYP1A1*2B. The frequency of this allele supposedly at-risk for lung cancer was significantly higher than in Middle European populations, but lower than in the Far East.