A new method of assay was applied to the determination of pregnanediol in urines from patients in whom the presence of a placenta or a corpus luteum could be excluded. The normal variation of pregnanediol content in such urines was examined. It was shown that operative stress or the intravenous administration of corticotrophin caused an increased output of pregnanediol. Quantitatively significant amounts of urinary pregnanediol could not be detected after adrenalectomy nor did adrenalectomized patients respond to corticotrophin by an increased pregnanediol output. It is considered that the adrenal contributes to the pregnanediol found in urine and that the determination of urinary pregnanediol may be of value in the study of adrenal function.Pregnane-3a:20a-diol is a neutral steroid occurring in urine as a conjugate of glucuronic acid. It is a metabolite of progesterone. When progesterone is administered to human subjects, some 10-20% of the hormone can be recovered as urinary preg¬ nanediol. It is generally supposed that the excretion of urinary pregnanediol can be used as a measure of the progesterone produced by the corpus luteum and the placenta. Pregnanediol was first isolated from pregnancy urine by Marrian [1929]. Since then many methods have been proposed for its quantitative deter¬ mination in urine. As these methods have become more reliable, the changes in excretion during the menstrual cycle and pregnancy have been more clearly under¬ stood. It has also become evident that not all the pregnanediol in urine can be accounted for by the activity of either the corpus luteum or the placenta. The work of Engel, Thorn & Lewis [1941] showed that small amounts of authentic 5/?-pregnane3a:20a-diol could be isolated from a large volume of pooled normal male urine. These findings were supported by the work of Heard & Hoffman [1941] and of Westphal [ 1944]. The latter estimated that male urine contained 0-7 mg pregnanediol/1.Although a third source of urinary pregnanediol is now established, its origin has not been conclusively demonstrated. Some of the urinary pregnanediol is thought to originate from the adrenal. Many workers have found an increased pregnanediol output in patients suffering from adrenal disorders.