Orosomucoid (ORM) phenotyping was performed by isoelectric focusing and immunoprinting. The band patterns of desialyzed ORM indicated that the ORM system is controlled by two structural loci ORM1 and ORM2. In a total of 253 samples from two Caucasoid populations, five phenotypes determined by three polymorphic alleles, ORM1*1, ORM1*2, and ORM1*3 were identified. The ORM1*3 was characteristic of the Caucasoids. The ORM2 locus was monomorphic.