Monocytes and macrophages arise from common hematopoietic stem cell precursors in the bone marrow. After their recruitment to the peripheral blood system, they circulate there as monocytes. Stimulation can drive their differentiation into macrophages and their following migration to various tissues and organs. Macrophages are important effector cells of the primary immune response and are portrayed by a complexity of functions such as maintenance of tissue homeostasis and repair, and promotion and inhibition of inflammatory processes. Prostaglandin (PG) D2 is a lipid mediator that plays a crucial role in inflammatory processes during allergic reactions. After its release from mast cells it acts on two distinct G-protein coupled receptors. The role of PGD2 in inflammation is conflicting, by eliciting both pro- and anti-inflammatory reactions. As yet, the understanding of its actions on monocytes and macrophages is only modest. The aim of this study was to investigate the role of PGD2 receptors in the function of primary human monocytes and macrophages. Isolated human monocytes were differentiated into macrophages and functional assays such as Ca2+ flux, migration and internalization assays were performed. The effect of PGD2 on macrophage activation was determined. Here, we could show that both receptors were expressed on human monocytes and macrophages, but in a higher amount in the latter. While both receptors showed a comparable, high capacity of eliciting intracellular Ca2+ mobilization on monocyte-derived macrophages, internalization rates differed. Macrophages exerted a chemotactic activity towards PGD2. During macrophage activation, PGD2 lead to an increase in the secretion of pro-inflammatory cytokines in activated macrophages, without influencing the cell surface receptor expression. It is highly assumable that PGD2 elicits pro-inflammatory processes in macrophages that contribute to tissue injury in allergic diseases and asthma.