Basic chemistry of the water soluble intravascular contrast media and result of adverse reactions are reviewed. Prophylactic treatment is recommended as well. Hopefully this attempt will draw attention from all disciplines in a department of diagnostic radiology and its clinical coworkers with particular emphasis on the rationale, properties and indications of the lower-osmolar contrast media. Present evidence strongly suggests (but not yet conclusive) that low-osmolar contrast media will be safer than the conventional media with a reduced incidence of life-threatening of fatal 'idiosyncratic' reactions. Ionic media should not be used intrathecally.