Children with asthma living on the northern Mexico border suffer not only from the physical aspects of this condition, but also from the lack of a clear biomedical definition and treatment plan for the illness. An ethnographic study involving participant observation and focused interviews in Tijuana, Mexico, sought to understand the intersection of diagnostic uncertainties surrounding childhood asthma on the part of parents, particularly mothers, living in acute poverty. Environmental factors such as dust and insects in impoverished homes probably acted as asthma triggers among many of the children in the study. Furthermore, management of children’s asthma took place not only in biomedical clinics, but also in homes, traditional medical settings, and pharmacies, where mothers often sought remedies for their children’s asthma attacks on an emergency basis. In all treatment settings, including biomedical ones, they often faced significant barriers to effective care, including the misuse of antibiotics. Thus, the role of pharmaceutical sales clerks, as well as pediatric asthma specialists, is explored in this article.