1. The hypothesis that suppression of prostaglandin E synthesis by indomethacin exacerbates renal-clip hypertension in the rat was investigated in four groups of rats.
2. Indomethacin was shown to exacerbate hypertension in renal-clip animals.
3. Synthesis of prostaglandin E, determined by gas-liquid chromatography, was suppressed in medullary tissue from the hypertensive animals irrespective of indomethacin treatment.
4. The findings support the concept that prostaglandins participate in the blood pressure regulatory function of the kidney but pose a number of unsolved questions.