The expression of leukotriene B4 (LTB4) and leukotriene D4 (LTD4) receptors was determined, by binding assay, in HL-60 cells differentiated into the monocyte/macrophage, neutrophil, and eosinophil lineages. Monocyte/ macrophage- and neutrophil-differentiated cells developed specific LTB4 receptors with high affinities (Kd = 1.27 nM and 2.65 nM, respectively) and low affinities (Kd = 26.41 nM and 55.63 nM, respectively). These receptors were functional and specific as indicated by the ability of LTB4 to elicit an increase in intracellular calcium concentration antagonised by specific antagonists. Eosinophil-differentiated cells developed mainly LTD4 receptors (Kd = 41.91 nM), and stimulation with LTD4 induced an increase in intracellular calcium that was antagonised by a specific LTD4 antagonist. These results show, for the first time, that eosinophil-differentiated HL-60 cells express specific functional LTD4 receptors. These cells could be used for the study of the actions of peptidoleukotrienes on eosinophils, and for studies on the molecular mechanisms regulating LTD4 receptor expression.