Recent changes in the political economy of Nicaragua have resulted in significant advances in public health. The improvements are due to changes in the health system which include comprehensive health planning, regionalization of health services and popular participation in health education and mass drug administration programs. Traditional structural approaches to the study of national health systems can benefit from an analysis of the process of change. The research reported herein focuses upon struggles between instructional actors who would professionalize primary health care and those who promote popular participation in the planning and execution of primary care programs. An analysis of decision-making within the Sistema Nacional Unico de Salud illustrates the process whereby a health system undergoes structural change from within. The Nicaraguan case suggests that the changing configuration of health systems is a dynamic process and the result of negotiation among several constituencies amid changing conditions in the world system. The role of a government seeking to democratize health delivery within a socialist political economy is to create and promote constituencies for the popular model and thereby institutionalize the debate.