A 120-kDa oviduct-specific glycoprotein is synthesized and secreted into the oviductal lumen during estrogen dominance in the human. The objective of this investigation was to clone, sequence, and characterize the cDNA to this core protein. Rapid amplification of cDNA ends was used to clone a contiguous 3' CDNA end and 5' cDNA end. The total length of the cDNA was determined to be 2.2 kb by sequence analysis and exhibited a 92% sequence identity with the comparable overlapping baboon cDNA (1.2 kb). A high degree of homology was found to the N-terminal sequence of hamster oviductin and the partial sequence of a homologous baboon and bovine oviduct glycoprotein. Northern blots revealed a single mRNA species of 2.4 kb. Using RNA from various tissues of an estrogen-treated baboon, we found that the mRNA for the oviductal glycoprotein was present only in the oviduct. Hybridization was detected to an mRNA of similar size from oviductal tissue of the baboon, hamster, and mouse and to an mRNA of slightly smaller size in the rabbit, cow, and cat but not to any mRNA species from rat oviductal RNA. Slot-blot analysis showed that the message was present in significantly greater (p < 0.05) concentrations in RNA from oviductal tissue from the late follicular stage than from the early follicular, early or late luteal, or postpartum stages. In conclusion, we have isolated the complete cDNA for a human oviductal glycoprotein. The presence of significantly greater amounts of the mRNA during the late follicular phase of the menstrual cycle is consistent with the proposed estrogen control. The mRNA for the oviductal glycoprotein is present only in the oviduct of an estrogen-treated baboon, and a cross-hybridizing RNA is found in oviductal RNA from various mammals.