The organum vasculosum of the lamina terminalis has been implicated as the site of receptors mediating central responses of angiotensin II. Up to now, this had been based on indirect evidence, but direct visualization of angiotensin II at its site of action has now been achieved by the use of a biologically active fluorescent angiotensin II agonist. The ventricular surface of the organum vasculosum lamina terminalis showed intense fluorescence, which was virtually eliminated by an excess of unlabeled angiotensin II.