A discussion of fundamental issues pertinent to investigations of the assessment or assurance of the quality of medical care, with the goal of fostering interdisciplinary work in this area. The first fundamental issue is the relative efficacy and/or effectiveness of the personal medical care system versus other social systems or variables which produce changes in health status. When choosing measures with which to assess the quality of care, the analyst must be sure they are valid measures. Failure to do so will result in the expenditure of billions of dollars to fulfill invalid criteria which when compiled will produce no change in health status. Although most of the paper is concerned with quality assessment methodology, the author points out that it is also important to raise and attempt to answer basic questions of quality assurance, a field in which there has been virtually no methodologic research. 38 pp. Ref.