The last decade of the twentieth century is witnessing a profusion of projects drawing together social and health scientists to study and recommend solutions for a wide range of health problems. The process--practiced in both developed and developing countries--is usually called multidisciplinary or interdisciplinary research. Its historical precedents are briefly reviewed in this paper along with the types of problems addressed. From a review and discussion of a sample of projects selected from two major proponents of this approach to research, the Social and Economic Research Component of the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases and the Applied Diarrheal Disease Research Project, conclusions are drawn about the nature of contributions from such efforts--very useful for short-term problem solving, less so for longer-term programmatic changes, especially beyond the health sector, and even more limited in impact on theory building for coping with the changing human condition. The recognition of such limitations is now widespread in the social and natural sciences beyond the health sector, in population, ecology, and the humanities. Following these observations, I argue for a new approach to transcend the disciplinary bounds inherent in multi- and interdisciplinary research. A transdisciplinary approach can provide a systematic, comprehensive theoretical framework for the definition and analysis of the social, economic, political, environmental, and institutional factors influencing human health and well-being. The academic and career challenges for such researchers, while considerable, may be overcome since there is now a new flexibility in research-supporting organizations to encourage new ideas in international health, such as that of essential national health research.