Genetic variation of orosomucoid (ORM) in the genus Macaca was investigated. Plasma samples were subjected to isoelectric focusing in a pH range of 4-6.5, followed by immunoprinting with anti-human ORM antibodies. A total of 25 alleles were identified in 231 Asian macaques belonging to 13 species from 23 populations and 22 members belonging to a family of M. fascicularis. Family data presented evidence for a codominant mode of inheritance with multi-alleles at a single autosomal locus. A population study revealed enormous intra- and interspecies variations. The heterozygosity values varied from 0.855 in M. fascicularis (Malaysia) to 0.000 in M. radiata (India), M. silenus (India) and M. arctoides (Malaysia).