The interactions of chemokines with their G protein-coupled receptors play critical roles in the control of leukocyte trafficking in normal homeostasis and in inflammatory responses. Tyrosine sulfation is a common post-translational modification in the amino-terminal regions of chemokine receptors. However, tyrosine sulfation of chemokine receptors is commonly incomplete or heterogeneous. To investigate the possibility that differential sulfation of two adjacent tyrosine residues could bias the responses of chemokine receptor CCR3 to different chemokines, we have studied the binding of three chemokines (eotaxin-1/CCL11, eotaxin-2/CCL24, and eotaxin-3/CCL26) to an N-terminal CCR3-derived peptide in each of its four possible sulfation states. Whereas the nonsulfated peptide binds to the three chemokines with approximately equal affinity, sulfation of Tyr-16 gives rise to 9-16-fold selectivity for eotaxin-1 over the other two chemokines. Subsequent sulfation of Tyr-17 contributes additively to the affinity for eotaxin-1 and eotaxin-2 but cooperatively to the affinity for eotaxin-3. The doubly sulfated peptide selectively binds to both eotaxin-1 and eotaxin-3 approximately 10-fold more tightly than to eotaxin-2. Nuclear magnetic resonance chemical shift mapping indicates that these variations in affinity probably result from only subtle differences in the chemokine surfaces interacting with these receptor peptides. These data support the proposal that variations in sulfation states or levels may regulate the responsiveness of chemokine receptors to their cognate chemokines.