Serious systemic reactions caused by currently used ionic and nonionic contrast materialare the anaphylactoid (allergic-like) reaction and the vagal reaction. Each likely has more than one etiology, and certain patients are at higher risk for developing such a reaction. The urologist I radiologist must be able to differentiate between the clinical manifestations of the anaphylactoid (asthma-like) reaction and the vagal (bradycardia and hypotension) reaction. Specific treatment for the anaphylactoid reaction is low-dose epinephrine; specific treatment for the vagal reaction is intravenous fluid and high-dose atropine.