In this paper the authors present a review of the multitudinous studies of researchers who have attempted to identify the sources of drug information utilized by physicians. Consideration is given to both professional sources (for example, journal articles, colleagues, meetings, and pharmacists) and commercial sources (for example, detailmen, journal advertisements, mail advertisements, and samples). Also included is a discussion of the relationship between physicians' sources of drug information and their choice of drugs and of the relationship between the sources of information and the severity of the conditions being treated. The paper concludes with a brief review of some of the new sources of drug information being considered for utilization by the Food and Drug Administration.