In this report, we describe the isolation, molecular cloning, and characterization of a new member of the prolactin (PRL)-growth hormone (GH) family expressed in rat decidual tissue. A 29-kDa protein was isolated from medium conditioned by decidual explants. The protein possessed an affinity for concanavalin A and cross-reactivity with antibodies to two rat placental proteins, PRL-like protein-B (PLP-B) and PLP-C and with antibodies to human PRL. NH2-terminal sequencing of the isolated decidual protein indicated that it shared significant sequence identity with the NH2 terminus of PLP-C. The decidual protein was termed decidual prolactin-related protein (dPRP). A PLP-C cDNA was used to identify dPRP cDNAs from a rat decidual cDNA library. Nucleotide sequence analyses of the dPRP cDNAs predicted a mature protein of 239 amino acids, including a 28-amino acid signal sequence. The predicted dPRP amino acid sequence contains two putative N-linked glycosylation sites and 6 cysteine residues. The 6 cysteines are located in positions homologous to the cysteines of PLP-C and PRL. Additional sequence similarities with members of the PRL-GH family are evident. The dPRP gene was localized to rat chromosome 17, which also carries other members of the PRL gene family. Northern blot analysis showed that the dPRP cDNA clone specifically hybridized to a 1.0-kilobase mRNA. The relationship of dPRP with other members of the PRL-GH family and its putative role(s) in the physiology of pregnancy are discussed.