We have cloned a cDNA for the platelet activating factor (PAF) receptor by screening an HL-60 granulocyte cDNA library with degenerate oligonucleotide probes based on conserved sequences of rhodopsin-type receptors. The 342-amino acid receptor contains 7 putative transmembrane domains, but lacks sites for N-linked glycosylation at the N-terminus. Stably transfected fibroblasts expressing the cloned cDNA responded to sub-nanomolar PAF stimulation with calcium mobilization, which could be inhibited by the PAF antagonist L-659,989. The PAF receptor message was detected as a single species of approximately 4 kb in human placenta, lung, and differentiated HL-60 granulocytes. Expression of the cloned cDNA in undifferentiated HL-60 cells devoid of endogenous PAF receptor resulted in specific and saturable binding of the PAF antagonist WEB 2086 with a dissociation constant of 30.7 nM.