Professor Mendelsohn pioneered the concept that angiotensin acts at the local tissue level by direct analysis of peptide levels, by defining the anatomical locations of the relevant enzymes and receptors and by subsequent physiological studies. The modern investigation of the brain angiotensin system started with Mendelsohn’s seminal mapping of brain AT1 and AT2 receptors that directed much subsequent experimental elucidation of angiotensin’s central functions. These discoveries underlie contemporary concepts of the pathophysiology of hypertension, heart failure and renal disease and underpin their current treatment by ACE inhibitors and angiotensin antagonists. His group’s recent cloning of the AT4 receptor opens up a new field regarding regulation of learning and memory.