1. Saralasin and converting enzyme inhibitors SQ 20881 and captopril induced increases in plasma renin activity to greater than 14 ng h−1 ml−1 in 43 out of 44 patients with untreated renovascular hypertension when studied in the seated position and on normal sodium intake. This degree of response was absent in patients with normal-renin essential hypertension and present in only three out of 26 with high-renin essential hypertension.
2. Reductions of greater than approximately 9% in diastolic pressure in response to these three drugs occurred regularly in renovascular hypertension (95%) but also frequently in high-renin (65%) and normal-renin (26%) essential hypertension.
3. Prior sodium depletion abolished the specificity of the renin and depressor responses to angiotensin blockage for renovascular hypertension.
4. Some patients with bilateral renovascular and all with malignant hypertension also exhibited these responses to angiotensin blockade that are characteristic of unilateral renovascular hypertension.