The authors present an ethnoepidemiological study of diarrheal illnesses in 21 communities on the northern coast of Ecuador, where numerous social and environmental changes have taken place since 2001 due to a new highway. As communities realize that nature itself is changing, changes occur in their interpretations of health and disease, which the authors present through a taxonomic classification of diarrheal illnesses. Given the high incidence of diarrheal diseases, alternative concepts have emerged (as compared to those of biomedicine) in relation to causes, symptoms, and treatments. The non-biomedical and biomedical systems overlap, with mixtures of coexistence and resistance. Recognizing this reality means understanding a series of challenges for the official health system, including the indiscriminate use of antibiotics, non-use of health services for some diseases, and perceived relations between environmental contamination and the efficacy of modern and traditional medicines.