In the late 1960s, it was already known that hormones such as adrenalin, histamine, dopamine and serotonin stimulate specific responses in the cells of human beings and other organisms. But the mechanism by which cells perceive and respond to these hormones was shrouded in mystery. In 1969, Lefkowitz successfully attached a radioactive isotope of iodine to a form of the hormone adrenaline, enabling him to track its movements within an organism. By 1974, he observed the hormone interacting with a specific protein in the cell wall, the first of many such "G Protein coupled receptors" (GPCRs) he would identify in the next 15 years of groundbreaking research. In 1986, he and his associates at Duke University Medical Center succeeded in cloning and sequencing the gene for one of these receptors and found that it responds to adrenaline much as receptors in the eye register light. He has since identified a superfamily of receptor proteins that circulate back and forth through the cell wall, triggering the appropriate response to hormones and other stimuli. Roughly half of all medications in use today depend on the action of the receptors Dr. Lefkowitz discovered; they are used to treat everything from diabetes to depression. His discovery has been recognized with nearly every honor in American science, as well as the 2012 Nobel Prize in Chemistry. This podcast combines excerpts from the Academy of Achievement's 2014 interview with Dr. Lefkowitz with highlights from his address to the 2014 International Achievement Summit in San Francisco.