Over the past decade, different parties in the health care field have developed and disseminated clinical practice guidelines as part of evidence-based medicine. These formal tools based on a scientific evaluation of the research literature purport to tell health care professionals how to practice medicine. Because clinical practice guidelines shift the knowledge base in the health care field through standardization, they remain controversial within and outside medicine. In this paper, we evaluate the predictive accuracy of four medical professionalization theories--functionalism, Freidson's theory of professional dominance, deprofessionalization theory, and the theory of countervailing powers--to account for (1) the shift from pathophysiology to epidemiology with guidelines, (2) the creation of practice guidelines, and (3) the effects of clinical practice guidelines on the autonomy of health professionals. In light of the mixed predictive record of professionalization theories, we conclude with a need for "evidence-based sociology" and a recalibration of basic premises underlying professionalization theories.