Leukotriene B-4 (LTB4)(1) is a potent chemoattractant that is primarily involved in inflammation, immune responses and host defence against infection(2). LTB4 activates inflammatory cells by binding to its cell-surface receptor (BLTR)(3). LTB4 can also bind and activate the intranuclear transcription factor PPAR alpha, resulting in the activation of genes that terminate inflammatory processess(4). Here we report the cloning of the complementary DNA encoding a cell-surface LTB4 receptor that is highly expressed in human leukocytes. Using a subtraction strategy, we isolated two cDNA clones (HL-1 and HL-5) from retinoic acid-differentiated HL-60 cells. These two clones contain identical open reading frames encoding a protein of 352 amino acids and predicted to contain seven membrane-spanning domains, but different 5’-untranslated regions. Membrane fractions of Cos-7 cells transfected with an expression construct containing the open reading frame of HL-5 showed specific LTB4 binding, with a K-d (0.154 nM) comparable to that observed in retinoic acid-differentiated HL-60 cells. In CHO cells stably expressing this receptor, LTB4 induced increases in intracellular calcium, D-myo-inositol-1,4,5-triphosphate (InsP(3)) accumulation, and inhibition of adenlyl cyclase. Furthermore, CHO cells expressing exogenous BLTR showed marked chemotactic responses towards low concentrations of LTB4 in a pertussis-toxin-sensitive manner. Our findings, together with previous reports(4,5), show that LTB4 is a unique lipid mediator that interacts with both cell-surface and nuclear receptors.