On neutrophil stimulation, the cytosolic components of NADPH oxidase, p67phox, p47phox, p40phox, as well as the Ras-related G-proteins Rac1 and Rac2, are translocated from the cytosol to cell membranes where they associate with a flavocytochrome b, forming a functional complex responsible for the production of oxygen radicals in phagocytes. In this paper we show that (a) in neutrophils from a patient with a form of chronic granulomatous disease (CGD) in which p67phox is absent, p47phox and Rac2, but not p40phox and Rac1 were translocated from the cytosol to the membrane on stimulation with formylmethionyl-leucylphenylalanine (fMLP) or phorbol 12-myristate 13-acetate (PMA); (b) in neutrophils from a patient with a form of CGD in which p47phox is absent, p67phox, p40phox and Rac1 failed to associate with the membrane on stimulation with fMLP or PMA, whereas Rac2 was translocated as in normal neutrophils. We also show that in neutrophils from a patient lacking p67phox, the amount of cytosolic p40phox was decreased by about 40%. These findings indicate that, on neutrophil stimulation, p67phox mediates the translocation of p40phox and Rac1 from the cytosol to cell membranes and that Rac2 associates with the membranes independently of p47phox and p67phox.