1. The anti-hypertensive effect of atenolol was greater than that of bendrofluazide.
2. The change in systolic blood pressure caused by bendrofluazide showed a significant inverse correlation with the plasma renin concentration (r = −0·47; P < 0·01).
3. The correlation between the change in systolic blood pressure caused by atenolol and the plasma renin concentration was not significant (r = 0·28; 0·1 > P > 0·05).
4. Plasma renin concentration was unaffected by atenolol.