The study hypothesis is that left-sided donor nephrectomy (i.e. with transaction of the adrenal vein) is deleterious to the left adrenal gland and causes a measurable transient adrenal insufficiency after the operation. The primary study endpoint is the assessment of adrenal function after donor nephrectomy. This is done by an ACTH stimulation test, performed at baseline, in the first week after the operation and 4 weeks after the operation. Comparisons are performed between baseline and postoperative values, as well as between left-sided kidney donors (n=20) and right-sided kidney donors (n=10). A secondary study endpoint is to assess the morphological response of both adrenal glands after donor nephrectomy. To this end MRI and volumetry of the adrenal glands is performed at the same time points, with the hypothesis that left-sided nephrectomy will lead to an involution of the left adrenal followed by hypertrophy of the right adrenal.