Using a modified Boyden chamber the effect of three antiinflammatory drugs on the chemotaxis of human neutrophils has been tested in vitro. Gold salt produced a reduction of both neutrophil migration and the ability of plasma to attract this cell. Betamethasone decreased chemotaxis by an action on the cell itself but not on the plasma. Aspirin had no effect on this function. These data suggest that antiinflammatory drugs act through different mechanisms and that the reduction of neutrophil chemotaxis may contribute to the antiinflammatory action of gold salts.