ABSTRACTObjective: The importance of the lymphatic system during inflammatory response is underscored by the discovery that numerous inflammatory mediators alter the lymph pump. Inhibition of the lymph pump will reduce the lymphatic outflow from the interstitial space and thus initiate the lymphatic generation of edema. We evaluated the effect that reactive oxygen metabolites have on the contractile activity of lymphatic vessels.Methods: Reactive oxygen metabolites are produced during inflammation and have been implicated in a number of pathologies. Exposure to reactive oxygen metabolites inhibited the lymph pump flow in a time‐ and concentration‐dependent fashion by decreasing contraction frequency, strength, and propagation.Results: Substance P (SP) (1.0 μM) produced the following changes (% control): reductions in diastolic diameter (56%), systolic diameter (47%), and stroke volume of the lymph pump (62%); a large increase in lymphatic contraction frequency (640%); and a modest increase in lymph pump flow (43%). SP also stimulated quiescent vessels to develop typical contraction‐relaxation patterns. These effects may serve to minimize the formation of edema in the face of inflammatory edemagenic conditions that are produced by SP.Conclusions: We concluded that reactive oxygen metabolites significantly inhibit the active lymph pump and that this inhibition could be an important contributing factor in the formation of interstitial edema during inflammation. We have also determined the effects of a putative mediator of inflammation (SP) on the lymphatic pumping function.