The actions of platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) are mediated through the PAF receptor (PAFr), which is a member of G-protein coupled superfamily of receptors. Our laboratory has data showing PAF has a role(s) in reproduction in domestic animals. Porcine, bovine and caprine PAFr genes cloned in BAC vectors were sequenced. Each PAFr coding sequence (cds) in these three species is 1029 nucleotides long and contains no intervening sequences. The deduced amino acid sequences (AAS) appear to contain seven putative transmembrane domains with an extracellular N-terminus in each species. There is a common glycosylation site at the fourth asparagine residue of N-terminus. In the tail of each deduced amino acid sequence, five to six serines and five threonine residues could act as phosphorylation sites, which play an important role in rapid receptor desensitization. The degree of homology of the three species is from 89 to 96% in nucleotide sequences (NtS), and 87-96% in identities (I) and 94-97% in positives (P) in amino acid sequences (AAS). The degree of homology with human, guinea pig, mouse and rat is 84-87, 82-88 and 83-88% in NtS, 77-84 (I) or 85-90 (P), 77-84 (I) or 85-90 (P) and 75-83 (I) or 87-90% (P) in AAS for caprine, bovine and pig, respectively. Southern blotting results suggested that the PAFr gene exists as a single copy in the genome of pig.