Henry Knowles Beecher, an icon of human research ethics, and Timothy Francis Leary, a guru of the counterculture, are bound together in history by the synthetic hallucinogen lysergic acid diethylamide (LSD). Both were associated with Harvard University during a critical period in their careers and of drastic social change. To all appearances the first was a paragon of the establishment and a constructive if complex hero, the second a rebel and a criminal, a rogue and a scoundrel. Although there is no evidence they ever met, Beecher’s indirect struggle with Leary over control of the 20th century’s most celebrated psychedelic was at the very heart of his views about the legitimate, responsible investigator.That struggle also proves to be a revealing bellwether of the increasingly formalized scrutiny of human experiments that was then taking shape.