Premedication with corticosteroids, H1/H2 -blockers and the use of low osmolality CM is beneficial in preventing nonidiosyncratic reactions during intravascular administration. However their role in during ERCP is unclear as CM is not injected into the intravascular space. Currently there are no formal recommendations and clinical practice varies considerably. The general purpose of this study is to determine the incidence of CM reactions during ERCP and to determine whether various risk factors are predictive of idiosyncratic reactions. Based on these results, we hope to develop guidelines for the use of prophylaxis to prevent CM reactions in ERCP.