Abstract The human CC chemokine leukotactin-1 (Lkn-1) is both a strong chemoattractant for neutrophils, monocytes, and lymphocytes and a potent agonist for CCR1 and CCR3. However, human neutrophils do not migrate when the cells are stimulated with other human CC chemokines, such as human macrophage inflammatory protein-1α (hMIP-1α) and eotaxin, which also use the CCR1 and CCR3 as their receptors. In this report, we demonstrate that while hMIP-1α induced a negligible level of calcium flux and chemotaxis, Lkn-1 produced a high level of calcium flux and chemotaxis in human neutrophils. Lkn-1 cross-desensitized hMIP-1α-induced calcium flux, but hMIP-1α had little effect on the Lkn-1-induced response in human neutrophils. The same pattern was observed in peritoneal neutrophils from wild-type mice, whereas neutrophils from CCR1−/− mice failed to respond to either MIP-1α or Lkn-1. Scatchard analysis revealed a single class of receptor for both hMIP-1α and Lkn-1 on human neutrophils with dissociation constants (Kd) of 3.2 nM and 1.1 nM, respectively. We conclude that CCR1 is a receptor mediating responses to both MIP-1α and Lkn-1 on neutrophils and produces different biological responses depending on the ligand bound.