Tritiated estradiol injected intravenously into 11 mongrel dogs sacrificed at 3, 7, 10, 17, and 60 min showed maximum uptake in the adrenal gland at 3-7 min. The concentrations of radioactivity in the adrenal in percent dose per gram equaled that from 131I-19-iodocholesterol. If a 131I-estradiol could be synthesized that would concentrate similarly in the adrenal, it would offer the advantage of almost instantaneous imaging after the tracer injection and a lower radiation dose.