The objective of this study was to detect and characterize a secreted oviduct-specific glycoprotein (OGP) in the rhesus macaque (Macaca mulatta) and to compare the characteristics of this OGP to those previously characterized in baboons and women. Oviducts were obtained from untreated ovariectomized rhesus and from ovariectomized rhesus either treated with estradiol (E2) for 14 days or treated sequentially with E2 for 14 days and then with E2 plus progesterone (P4) for an additional 14 days. Segments of oviducts were either fixed for morphological analysis, cultured for OGP synthesis and release, or frozen for RNA analysis. The proteins present in the culture media were separated by one-dimensional SDS-PAGE, and OGP was detected on Western blots using polyclonal antibodies generated against the reduced form of baboon OGP or a 17-amino acid segment of the baboon core protein. Cross-reacting antigens were present in the 120-kDa region, identical to what was observed for baboon and human OGP. Indirect immunogold localization of OGP on thin sections demonstrated specific clustering of gold particles over the apical secretory granules of the secretory cells of the oviductal epithelium. A cDNA was generated using RT-PCR and 5' and 3' rapid amplification of cDNA ends (RACE), and sequenced. The total transcript was 2237 nucleotides in length plus a poly(A) tail. The largest open reading frame was 624 amino acids, which would produce a protein of 69.3 kDa. The nucleotide sequence was more than 95% identical to the nucleotide sequences of baboon and human OGP. Northern blots revealed a single message at 2.4 kilobases (kb) in oviduct samples obtained from E2-treated rhesus. This message was absent in oviducts obtained from untreated ovariectomized and from sequential E2 plus P4-treated rhesus macaques. In summary, the rhesus oviduct synthesizes and secretes an OGP in the presence of E2 that is immunologically and structurally similar to the baboon and human OGP. The presence of a highly homologous glycoprotein in several primates suggests a similar function for OGP in the reproductive process.