Antibodies are adaptor molecules of the immune system that link antigen recognition with the effector mechanisms responsible for antigen clearance. Several nonhuman primate species are widely used in biomedical research, especially for vaccine development and for AIDS-related studies. However, nonhuman primate antibody molecules have been characterized only partially and only in a few species. Here, we describe sooty mangabey (Cercocebus torquatus atys) IGHG and IGHA genes, which encode the heavy-chain constant region of IgG and IgA molecules, respectively. The four mangabey IGHG genes are highly homologous to the rhesus macaque and baboon IGHG genes (percent identity varies between 94.0 and 98.8, depending on the subclass), with most amino acid differences located in the hinge regions. Results obtained by real-time reverse transcription polymerase chain reaction show that the four IGHG genes are expressed at least at the mRNA level. The mangabey IGHA gene is highly homologous to the corresponding gene from rhesus macaques (percent identity ranges from 88.6 to 96.7, depending on the allele considered), the only other nonhominoid primate species for which the complete sequence of the IGHA gene is currently available. In the mangabey analyzed, two IGHA alleles are present, confirming that high levels of IGHA gene heterozygosity are present in monkey species. These results show that nonhuman primate gamma and alpha heavy chains differ from each other mostly at the level of the hinge region and that alpha sequence heterogeneity in nonhuman primate species is also present in other gamma regions. In addition, these results provide sequence information that can be used for residue frequency analysis of antibody heavy-chain constant region sequences.