1. Changes in systemic haemodynamics and organ blood flow were measured in conscious rabbits after various doses of intravenous sodium meclofenamate, an inhibitor of prostaglandin cyclo-oxygenase.
2. Meclofenamate had no effect on arterial pressure or cardiac output but caused a dose-dependent fall in renal blood flow.
3. Meclofenamate also reduced adrenal perfusion but, in contrast, caused a dose-dependent increase in blood flow to the brain, bronchial and hepatic circulation and to the testis. No effect was demonstrated on other organs studied.
4. The effect on the cerebral circulation was observed at the lowest dose of meclofenamate (0.75 mg/kg). Higher total doses were necessary for an effect on the renal and bronchial (3 mg/kg) and testicular and hepatic arteries (6 mg/kg).
5. The results suggest a variety of local vasomotor influences of renal and non-renal prostaglandins in conscious rabbits.