Trafficking of dendritic cells (DCs) to peripheral tissues and to secondary lymphoid organs depends on chemokines and lipid mediators. Here, we show that bone marrow-derived DCs (BM-DCs) express functional leukotriene B4 (LTB4) receptors as observed in dose-dependent chemotaxis and calcium mobilization responses. LTB4, at low concentrations, promoted the migration of immature and mature DCs to CCL19 and CCL21, which was associated with a rapid (30-minute) increase of CCR7 expression at the membrane level. At longer incubation times (6 hours), gene array analysis revealed a promoting role of LTB4, showing a significant increase of CCR7 and CCL19 mRNA levels. BM-DCs cultured from BLT1-/- or BLT1/2-/- mice showed a normal phenotype, but in vivo BLT1/2-/-DCs showed dramatic decrease in migration to the draining lymph nodes relative to wild-type (WT) DCs. Consistent with these observations, BLT1/2-/- mice showed a reduced response in a model of 2,4-dinitro-fluorobenzene (DNFB)-induced contact hypersensitivity. Adoptive transfer of 2,4-dinitrobenzene sulfonic acid (DNBS)-pulsed DCs directly implicated the defect in DC migration to lymph node with the defect in contact hypersensitivity. These results provide strong evidence for a role of LTB4 in regulating DC migration and the induction of adaptive immune responses.