There are many unanswered questions about the mechanisms and prevention of adverse reactions to RCM. Serious reactions will likely occur less often in your experience if you observe these precautions: 1. Consider that every patient is a candiate for an adverse reaction when you request the contrast study. 2. Be particularly cautious in performing the study in those with previous reactions to RMC, those who are strongly atopic, and those in whom intravenous cholangiography is planned. Look for alternative diagnostic approaches in treating these individuals. 3. If there is any likelihood of increased reactivity, inform the patient, carry out a study with intravenous infusion in place and appropriate physician observation during and after the study, consider prestudy treatment with antihistamines and/or steroids, and be prepared to institute emergency measures should the need arise.