Polymorphism of thyroxine-binding prealbumin (TBPA) in the rhesus monkey is controlled by 2 co-dominant alleles, PAF and PASF. According to Tanake et al (1974) tetrameric, TBPA occurred only in the Catarrhini but not in the Platyrrhini spp. was widely present in cercopithecoid spp. but was monomorphic and fixed homozygous F (PAF/PAF) in hominoids. Plasma samples collected from hamadryas baboon (Papio hamadryas), doguera baboon (Papio anubis), natural hybrids between P. hamadryas and P. anubis and savannah (grivet) monkey (Cercopithecus aethiops), (all from Ethiopia), human (Homo sapiens), chimpanzee (Pan trogrodytes), Japanese monkey (Macaca fuscata fuscata), Moore monkey (M. maura), red-faced monkey (M. speciosa), pig-tailed monkey (M. nemestrina), Formosan monkey (M. cyclopis) rhesus monkey (M. mulatta), bonnet monkey M. radiata, crab-eating monkey (M. irus), Assam monkey M. assamensis and mona monkey C. mona were collected and used for TBPA analysis. No individual having PAs was observed in the hominoids examined. In the hominoids including 2 families of Homininae and Hylobatidae, phenotypes of TBPA seemed fixed to homozygous F (PAF/PAF).