CCR1 is a GPCR that binds to a variety of CC ligands, including MIP-1a, RANTES, MCP-3, HCC-1, HCC-2, HCC-4, and MPIF-1 (Olson and Ley, 2002). Lymphocytes, macrophages, dendritic cells, and GM-CSF-activated neutrophils express CCR1 (Kaufmann et al., 2001; Cheng et al., 2001). Two selective, non-peptide small molecule antagonists of CCR1, BX-471 and CP-481,715, have been synthesized (Gladue et al., 2003; Liang et al., 2000). Pharmacological and genetic targeting of CCR1, either alone or in combination with cyclosporin A, reduces cardiac and renal allograft rejection (Gao et al., 2000; Horuk et al., 2001a; Horuk et al., 2001b), allergic encephalomyelitis (Liang et al., 2000), and renal fibrosis (Anders et al., 2002) in experimental models. Cloned human CCR1-expressing cell line is made in the Chem-1 host, which supports high levels of recombinant CCR1 expression on the cell surface and contains high levels of the promiscuous G protein Ga15 to couple the receptor to the calcium signaling pathway. Thus, the cell line is an ideal tool for screening for antagonists of interactions between CCR1 and its ligands.