There is an expanding need for quantitative information to evaluate health and medical care procedures. Existing methods for designing and carrying out evaluation studies need to be improved to provide better techniques for answering questions on efficacy of health and medical procedures, and in providing a more adequate information base on which to set health policy. This paper reviews some of the problems in the design and conduct of evaluation research, and makes a plea for creation of a special discipline to support and develop the field of health and medical care evaluation.