AbstractResearch of all types plays a fundamental role in setting health care priorities, in part by informing the development of robust clinical practice guidelines. Today's investments in research may make tomorrow's choices about who gets what kinds of care easier, not more difficult. The converse also holds: today's investments in providing care, if made at the significant expense of research, will not make tomorrow's choices about care any easier. In making choices and balancing priorities, the centrality of health services research must be understood. The information necessary to make the hard choices about priorities in health care today may be generated as much, if not more, from investments in this field of inquiry as from equivalent investments in other arenas of scientific endeavour, because of the growing need for information about the effectiveness of health care services for use both in improving the quality of health care and in making better use of health resources.