Functional dynamic studies of the adrenal in vivo employing 131I-19-cholesterol were carried out as a further screening test, according to the method previously described (Pavonia and Magrini, 1977), on seven patients in whom hyperadrenocorticism was suspected on the basis of clinical symptoms. The data obtained in basal conditions, under ACTH stimulation, and under dexamethasone suppression, compared with each other and supported by the results of conventional examinations, demonstrate that the quantitative information provided by this radioisotope test is correlated with the functional state of each adrenal, thus confirming the potential value of the method for diagnostic purposes. The functional dynamic test proposed does not require a higher dose of tracer than morphologic studies and the radiation risk (approximately 2.5 rad to the ovaries or gonads) seems acceptable in adult subjects.