PIP: New global and national health challenges require a new response. National health situations are increasingly influenced by the international transfer of health risks posed by environmental threats, overuse of resources, international migration, trade in harmful legal products (tobacco), traffic of illicit drugs, and diffusion of potentially inappropriate and costly medical technologies and treatment policies. This situation calls for reform of national health systems, and a natural extension of such reform is reform of the world health system. The first step toward this goal should be to achieve consensus about the essential core functions of international health organizations their division of labor. Currently international health agencies have overlapping mandates and duplicate efforts, and they have neglected the following essential functions: monitoring emerging diseases, setting consumer health standards, providing international coordination to control the transfer of health risks, coordinating research efforts and technological development, designing information systems to facilitate development of national and global health policies, accumulating knowledge about cost-effectiveness of medical technologies and interventions, and creating a process for sharing information about national health system reform. Reform "essentialists" identify the following core functions for international health organizations: surveillance and control of globally-threatening diseases, promotion of research and technological development, development of standards and norms for international certification, protection of international refugees, and assisting vulnerable populations. Others give international health organizations a more expansive role including redistributing resources from rich to poor countries, political advocacy, direct regulation of transnational corporations, and intervention in national health projects. Consensus must be reached to effect reform.