As a result of the demographic and epidemiological transitions now occurring rapidly in many developed countries, a dramatic shift in the age structures of populations and the burden of disease towards the middle-aged and elderly is expected to take place over the next several decades. In the 1990s, however, there remains great diversity across countries in fertility levels and mortality patterns. The World Bank's 1993 World Development Report assessed the global burden of disease in order to define the minimum packages of public health measures and clinical interventions that would improve health conditions in low-income countries in a cost-effective and affordable way. Strategically implementing these programmes will require that government investments be directed toward a limited number of cost-effective health interventions, delivered equitably to the entire population. At the same time, steps must be taken to improve the efficiency and contain the costs of health care delivery in the public and private sectors. Such a population-based health strategy will require the development of a wide range of scientific, analytical and technical capacities, currently rare in most ministries of health. This will require the involvement of epidemiologists, demographers, sociologists, analysts, operations research specialists and environmental health scientists. Building up these capabilities in health ministries, universities or the private sector will be an essential ingredient of health system reform.