Henry K. Beecher and Maurice H. Pappworth were the 2 most prominent medical whistleblowers in research ethics of the 20th century. Independently,both wrote highly controversial and ultimately influential articles and books. Although their work is now well-known in clinical research circles,their collaboration is not. Pappworth’s article “Human Guinea Pigs:A Warning”was published in 1962;in it,he discussed a series of published studies that he considered unethical. Beecher read it and wrote to Pappworth seeking help. The current article reconstructs,from Beecher and Pappworth’s correspondence in 1965–1966,an important juncture in the genesis of modern clinical research ethics. Although they shared much in common,they differed radically in the strategies they adopted:Beecher chose to conceal the identities of individuals,whereas Pappworth believed that only by naming and shaming could any exposéact as a deterrent. Their correspondence reveals how the 2 men shared their ideas and their material and provided each other with much-needed support. It also tracks the development of Beecher’s shift from a position initially indistinguishable from Pappworth’s toward the one he adopted when his seminal article of 1966 was published.