The primary care physician needs to identify those patients with acute pharyngitis who require specific antimicrobial therapy and to avoid unnecessary and potentially deleterious treatment in the large majority of patients who have a benign, self-limited infection that is usually viral. In most cases, differentiating between these two types of infection can be accomplished easily if the physician considers the epidemiologic setting, the history, and the physical findings, plus the results of a few readily available laboratory tests. When antimicrobial therapy is required, the safest, narrowest-spectrum, and most cost-effective drugs should be used. Despite agreement on these principles by expert advisory committees, data from national surveys of ambulatory care indicate that antimicrobial agents continue to be prescribed indiscriminately for upper respiratory infections.