The cloning and sequence analysis of Tibetan macaque IFN-(gamma) and the IL-6 cDNAs are described. The Tibetan macaque IFN-gamma and IL-6 cDNAs were found to be 498 and 639 bp in length, with open reading frames encoding 165 and 212 amino acids, respectively. Homology analyses indicated that the identity levels of nucleotide and deduced amino acid sequences of IFN-gamma among primates ranged from 93.4 to 99.2%, and 87.3 to 99.4%, respectively, and that of IL-6 ranged from 92.6 to 99.8%, and 85.4 to 99.5%, respectively. Phylogenetic analysis based on amino acid sequences showed that the Tibetan macaque is most closely related to Old World monkeys, as compared to Hominoidea and New World monkeys. These findings provide insights into the evolution of primate IFN-gamma and IL-6 and additional valuable information regarding amino acid residues essential for their biological activity.