Until recently, the production of reactive oxygen species by NADPH oxidase has been considered only in the context of the oxidative damage to pathogens inside the phagosome. However, homologues of phagocytic NADPH oxidase have been found in almost all cell types, where they produce hydrogen peroxide and thereby regulate the initial intracellular stages of MAP kinase cascades. In the present work, the activation of two MAP kinase cascades, p38 and Erk1/2, during phagocytosis has been studied. It was found that phagocytosis activates both cascades. The activation of Erkl/2 is dependent, and the activation of p38 is not dependent, on the activity of NADPH oxidase. Thus, it can be stated that the activation of MAP kinases in phagocytes during phagocytosis occurs by a mechanism similar to that operating in nonphagocytizing cells, indicating the universality of the function of NADPH oxidases in different cell types.