1. The functional integrity of the adrenal cortex has been tested in a case of selective hypoaldosteronism by adrenocorticotrophin (ACTH) and angiotensin II (AII) infusion.
2. During ACTH infusion a normal functioning zona fasciculata was indicated by the impressive increase of the ACTH-dependent plasma steroids; the aldosterone response was moderate.
3. During AII infusion the plasma aldosterone response was blunted with an unexpected dose-dependent increase in pregnenolone, resulting in abnormal decreasing progesterone/pregnenolone ratios during the infusion, suggesting a slow-down in the conversion of pregnenolone into progesterone.
4. This defect, a probable consequence of chronic renin deficiency on the zona glomerulosa, could be a contributing factor to the hypoaldosteronism.