In March of 1900 several cases of bubonic plague were discovered in San Francisco's Chinatom. In response the health authorities, at the instance of the Surgeon General of the United States, sought to implement a series of extraordinarily coercive measures aimed at the city's Asian inhabitants. The measures provoked an uproar among the Chinese, and they determined to challenge them in the federal Circuit Court for the Northern District of California. This essay, based on extensive research in court records, the archives of the U.S. Public Health Service, and press accounts in English and Chinese, documents the complex events that gave rise to the cases of Wong Wai v. Williamson and Jew Ho v. Williamson and the cases themselves as they unfolded in the courts. The cases raised new and dificult questions of fact and of law and tested as few other cases have before or since a court's capacity to act as arbiter between individual rights (and the rights of an ostracized minority at that) and the public interest in a period of acute health emergency.