CCR6 is the only known receptor for the chemokine macrophage-inflammatory protein (MIP)-3α/CC chemokine ligand (CCL) 20. We have shown previously that CCR6 is expressed on peripheral blood B cells, but CCR6 activity on these cells is low in in vitro assays. We report that MIP-3α/CCL20-induced calcium flux and chemotaxis can be enhanced significantly on peripheral blood and tonsillar B cells after activation by cross-linking surface Ag receptors. Of particular interest is the fact that the enhanced activity on B cells was not associated with an increase in CCR6 expression as assessed by levels of receptor mRNA, surface staining, or MIP-3α/CCL20 binding sites, or by a change in the affinity of the receptor for ligand. These data convincingly demonstrate that responses to a chemokine can be regulated solely by changes in the downstream pathways for signal transduction resulting from Ag receptor activation, and establish CCR6 as an efficacious receptor on human B cells.