Detailed understanding of chemokine action ultimately requires molecular cloning of chemokine receptor genes and cDNAs. Both forward and reverse genetic methods have been used for this purpose (1). Forward methods, which involve primary purification of a protein based on a defined physical or functional property, has been used for only one chemokine receptor, the Duffy antigen receptor for chemokines, and was actually used before Duffy was shown to bind chemokines (2). Reverse methods, which involve cloning a cDNA or gene without primary knowledge of the structure of the encoded protein, can be divided into two types: expression and homology hybridization cloning.