To thoroughly detail adverse reactions that may take place following the administration of agents used to modify behavior or to control fear and anxiety is beyond the scope of this presentation. Nevertheless, an attempt has been made to examine the mechanism of action, preventative measures, and management techniques for a few of the most common adverse reactions involving the more popular agents. Emphasis has been placed on the prevention of pharmacologic misadventures rather than on their management. The taking of an adequate pretreatment history and physical examination (including blood pressure determination) is invaluable in this respect. On occasion, however, despite all precautions and preventative measures, problems can arise. I have emphasized the mechanical, or nonpharmacologic approach, to the management of adverse reactions. Because untoward events occur so infrequently, the nonpharmalogic approach is the safest, most effective way for the clinician to cope with the majority of problems that can arise. The need for all practitioners to be competent in the management of the unconscious patient cannot be overemphasized. Production of unconsciousness is the most serious reaction with which the dentist is likely to be confronted on a routine basis. Mismanagement of this relatively benign state can, and on occasion does, result in deterioration to a catastrophic conclusion. It must also be emphasized that in the face of serious adversity the first few moments are usually the most critical in determining the final outcome. Although the summoning of assistance may be necessary and appropriate, one must not rely on the arrival of "emergency teams" to resolve the problem. If serious sequelae are to be avoided, proper management procedures must be instituted immediately and continued until medical assistance arrives and definitive care can be instituted. Thorough understanding of the pharmacology of all agents employed during the course of dental care is the key to the prevention and management of adverse drug reactions.