This paper seeks to describe two important ‘market’ systems in health – treatment and disease transmission – in which international development actors have sought to intervene to improve health outcomes in developing countries. Donors may be seen to perform a direct role in delivering or supporting delivery of health goods and services, or to take a systemic approach that avoids any such direct role. The argument is that, while sometimes beneficial, there are shortcomings with direct interventions that predominate in health, and the nature of those benefits or shortcomings depends on four considerations related to the treatment and transmission systems: the nature of the health problem, the scale of intervention impact, the requirement for ongoing provision, and the importance of individual agency in the transaction. The paper briefly describes the systemic approach to development intervention before looking at examples from Kenya and Tanzania of innovative programming in the health sector that has begun to apply such an approach. While more evidence is required in order to explain the determinants of health intervention success or failure, it is nevertheless possible to suggest that the importance of ensuring ongoing provision and accounting for individual agency is underestimated. For ongoing health problems with an important demand-side component, a sustainable and locally responsive system for delivery of treatment and control of transmission is required.