Catastrophic and shock life reactions and fatalities in intravenous urography continue to be poorly understood. We propose to investigate the possibility of two factors acting simultaneously in causing these reactions, one factor being the administered contrast material, the other being a drug or altered body state. Dogs will be given drugs which will place the animal in an altered state of reactivity as determined by the repetitive ventricular response to single monophasic pulses delivered to the right ventricle by an intracardiac electrode introduced via the jugular vein. The effect of the intravenous urographic contrast medium during the altered body reactivity will be observed. Digitalis, phenothiazine, and psychologic stress capable of changing body reactivity will be examined. Preliminary evidence indicates that digitalis plus contrast material produces cardiac arrhythmias. Through assembly of this type of evidence, patients at higher risk may be defined so that precautions may be taken or close monitoring be performed.