Arylamine N-acetyltransferases (NATs) are encoded at two loci on 8p22, a region subject to deletions in bladder tumours. The two functional genes (AAC1 and AAC2 alias NAT1 and NAT2) without introns in the coding region, encode enzymes which metabolise carcinogens, including bladder carcinogens. They are both multi-allelic and certain alleles have been implicated as susceptibility factors in bladder cancer. There is a third N-acetyltransferase gene, a pseudogene, AACP alias NATP, which we show is also located on chromosome 8 at the p22 region. We have mapped a series of YAC clones (ICI and CEPH) containing the NAT genes and the markers D8S21, an RFLP marker, and D8S261, a microsatellite marker. We show that D8S21 is a portion of the coding region of AAC2. The order of genes in this region, covering some 2 Mb, is TEL-D8S261-AAC1-AACP-AAC2 (D8S21)-CEN. The restriction map also illustrates that there are likely to be other expressed genes in the region through the identification of CpG islands.