A study was made of flunixin meglumine, an analgesic agent with antiinflammatory and antiprostaglandin activity, for the management of endotoxin-induced cardiovascular derangements. Three groups of 5 ponies each were used: controls--group 1; given endotoxin but not treated--group 2; and given endotoxin and treated with flunixin meglumine--group 3. Shock was induced in anesthetized ponies with IV injection of Escherichia coli endotoxin. Hemodynamic changes were monitored, and regional blood flow was determined at 4 different times, using microspheres labeled with 1 of 4 nuclides. There were extensive vasodilation and decreased blood return to the heart of group 2 ponies, as indicated by decreased mean arterial blood pressure and central venous pressure and by increased heart rate and cardiac output. Blood flow, as determined by radioactive microspheres, to gastrointestinal regions, skeletal muscle, and skin was increased and that to the CNS was decreased. Treatment with flunixin meglumine (group 3 ponies) exerted selective microvascular actions which helped to reverse endotoxin-induced changes. This included the maintenance of mean arterial blood pressure and the enhanced perfusion of vital organs (eg, brain and heart) by preventing extensive vasodilation in the gastrointestinal tract.