Gabriela Soto Laveaga examines how the global search for medicinal plants transformed Mexico into the world’s supplier of synthetic steroid hormones. The search for barbasco, a Mexican wild yam, revolutionized pharmaceuticals, paving the way for some of the twentieth century’s most important medications, including cortisone, antihistamine, and oral contraceptives. Focusing on the southern state of Oaxaca, Soto Laveaga examines the more than 150,000 men, women, and children who from the 1940s to the1970s harvested these wild yams without realizing their medical and financial potential. In so doing she challenges us to consider what is “science” and who can produce it.