This study examined the dependence of neurogenic and non-neurogenic synovial plasma extravasation on neutrophils. Perfusion of bradykinin into the knee joint produced both a rapid increase in the magnitude of plasma extravasation and a significant increase in number of neutrophils in the synovium. Both bradykinin-induced plasma extravasation and neutrophil accumulation were dependent on sympathetic post-ganglionic neuron terminals, since both were blocked in sympathectomized rats. Platelet activating factor, which produces plasma extravasation independent of sympathetic neurons, did not increase the number of neutrophils in the synovium. These findings support the suggestion that bradykinin acts on sympathetic nerve terminals in the knee leading to attraction of neutrophils, which promotes plasma extravasation.