The human alpha(1)-acid glycoprotein (AGP) or orosomucoid (ORM) is controlled by the two tandemly arranged genes, AG;PI and AG;PS. The further duplication of the AGP1 gene has been suggested by a few duplicated ORM1 locus haplotypes including ORM1*F1 . S and ORM1*B9 . S, detected by isoelectric focusing. To clarify the triplication of the AGP gene, 39 DNA samples from Japanese subjects were studied by the long-range PCR of intergenic regions. The analysis of PCR products showed that the tandemly triplicated genes, AGP1A-AGP1B-AGP2, occurred on about 20% of chromosomes. These composites were divided into ORM1A*F1-ORM1B*S-ORM2*M and ORM1A*B9-ORM1B*S-ORM2*M by allelic variations. Furthermore, the former was classified into a few haplotypes by three synonymous sequence variations, which might have arisen through gene conversion-like events. The recombination breakpoints existed between the 5' flanking region and intron 2 of the AGP1B gene. Thus, it is likely that the rearrangement of the AGP gene has Often occurred.