Two nonsteriodal antiinflammatory agents, indomethacin and meclofenamate, were found to produce a marked decrease in mesenteric blood flow, an increase in blood presure and no significant change in celiac blood flow. The initial effect of indomethacin on mesenteric blood flow differed from that seen with meclofenamate. Whereas meclofenamate induced a fall in mesenteric blood flow that was gradual in onset, indomethacin induced a marked vasoconstriction of the mesenteric bed that was immediate in onset and of short duration, which was followed by a decrease of slower onset similar to that seen with meclofenamate.