In the 1940s, US and Guatemalan doctors working with the Pan American Sanitary Bureau (PASB) intentionally exposed at least 1,308 Guatemalan sex workers, prisoners, hospital patients, and soldiers to three sexually transmitted infections (STIs)—syphilis, gonorrhea, and chancroid. The doctors aimed to study the transmission of disease and the effects of penicillin and other chemical solutions in preventing the spread of STIs. This article examines how US and Guatemalan doctors weaponized a bureaucratic registration system to study STIs at what they deemed their main vector—sex workers. The experiments served the purposes of the Guatemalan Revolution (1944–54), a democratizing moment when doctors and political leaders aimed to spur national regeneration. This essay argues that Guatemala's activist state was a critical enabling factor granting US researchers access to Guatemalans' genitals and blood for experimentation.