Activation of superoxide-generating NADPH oxidase system of human neutrophils involves phosphorylation-dependent translocation of p47phox and other cytosolic components to the plasma membrane. In contrast to the stimulation of the NADPH oxidase in intact cells, however, the activation of cell-free system requires the addition of anionic amphiphiles such as sodium dodecyl sulfate (SDS) and arachidonate. In this system, translocation of p47phox is also an essential step for activation, but phosphorylation is not required. The basis of this difference in oxidase activation is not yet clear. We now report that in a cell-free oxidase system, phosphorylated recombinant p47phox can be translocated to the membrane in the absence of SDS or arachidonate. These findings suggest that both phosphorylation and SDS could cause a common change in conformation or charge of p47phox that may result in the association of p47phox with the plasma membrane.