Magnesium is highly involved in the metabolic network such that even subtle disturbances in its homeostasis affect many cellular functions, including calcium homeostasis, signal transduction, energy metabolism, membrane stability and cell proliferation. Recently, magnesium level has been proposed to modulate the priming and activity of immune cells. We studied the behavior of antigen-presenting cells (APCs) and T lymphocytes after altering the magnesium/calcium balance. We used two different populations of primary APCs, i.e. bone marrow-derived dendritic cells and bone marrow-derived macrophages, while D10.G4.1 cells served as a model of responding Th2 cells. Our principal findings are the following: (i) the extracellular magnesium concentration had no significant impact on endocytosis by bone marrow-derived APCs, (ii) high concentrations of extracellular magnesium, with or without calcium antagonists, significantly decreased IL-4 and IL-10 secretion by Th2 cells in a co-culture system of APCs and Th2lymphocytes, (iii) proliferation of Th2cells in co-culture systems was significantly inhibited by calcium antagonists independently from extracellular magnesium concentrations. Our results suggest that alterations of magnesium and calcium homeostasis impact on some crucial steps of the immune response.