This is an attempt to present a comprehensive overview of two major trends in American medicine which suggests significant evolutionary biopsychosocial developments in the remaining decades of the 20th century. Comments have been confined to the U.S. because it is the geographical country of residence and practice of the authors, and because the U.S. appears to be the locus of two contemporaneous and seemingly antithetical popular movements: quantum leaps in the development and use of medical technology and a groundswell of interest and enthusiasm for health enhancement or wellness which advocates a natural approach to health and emphasizes the central role of the individual in the preservation of health and the prevention of illness. The dynamics of this modern dialectic in American medicine have generated important qualitative consequences in the nature of the doctor-patient relationship and the delivery of health care. They have also, it is submitted, generated the search for a new paradigm which will permit a workable equilibrium between the disparate imperatives of both movements. The delicate process of developing that equilibrium is made more difficult by the co-existence of a host of complex factors, many of which are inextricably interwoven with one or the other of these two major trends.(ABSTRACT TRUNCATED AT 250 WORDS)