The nucleotide (nt) and deduced amino acid (aa) sequences were determined for polymorphic arylamine N-acetyl-transferase (NAT2) and its gene, NAT2, from homozygous rapid and slow acetylator congenic Syrian hamsters. The slow acetylator (NAT2s) allele contained three point mutations which differed from the rapid acetylator allele (NAT2r); two mutations were silent, and the third mutation resulted in a premature stop codon. The NAT2s allele contained a truncated open reading frame of 726 nt encoding a 242-aa protein, which is 48-aa shorter than NAT2r.