Using inhibitors of arachidonic acid (AA) metabolism, the possible involvement of AA products in the generation of [Ca*'li and the pH, rise induced by the mitogen concanavalin A (Con A) in rat thymocytes has been studied. The lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA, 10 PM) and the phospholipase 4 inhibitor bromophenacyl bromide (10 PM) eliminated the [Ca*'k signal induced by Con A; the cyclooxygenase blocker indomethacin also inhibited it. However, neither NDGA nor indomethacin suppressed the pH, rise stimulated by Con A. Exogenous AA induced an increase in [Cazf]i but not in the pHi. These results indicate that AA metabolites, probably of the lipoxygenase pathway, take part in the generation of the [Ca2']r response to the mitogen. In contrast, they appear not to be involved in the pH, rise evoked by Con A.Arachidonic acid; Ca*+, cytosolic free; Concanavalin A; (Rat thymocyte)