1. When angiotensin II was infused into forty unselected subjects a linear relationship was found between the increment of diastolic blood pressure and the logarithm of the rate of infusion of angiotensin II.
2. The slope of this line was very reproducible on repeated determinations in the same subject.
3. When the correlations between pre-infusion plasma renin activity and various functions derived from dose—response curves were determined, it was observed that: (i) the significance of the correlation became progressively stronger when increasing thresholds of the pressor response to angiotensin II were considered; (ii) the best correlation was achieved when the slopes of the individual dose—response curves were plotted against the logarithm of corresponding plasma renin activities.
4. These results suggest that the slope of the pressor dose—response curve is the most reliable index of responsiveness to intravenously infused angiotensin II and that it may provide a satisfactory guide to the basal plasma renin activity.