[en] Purpose: To study potential properties of iodinated radiographic contrast media (IRCM) for intravascular use in in vitrfree radical generating reactions. Material and Methods: Superoxide (O₂^- ) and hydroxyl (OH) radicals were generated in xanthine oxidase and Fenton reactions. O₂ - was assayed by the nitroblue tetrazolium (NBT) method, whereas OH was assayed by an aromatic hydroxylation (2-hydroxy-benzoic acid) method. Total antioxidant status (TAS) of test substances was determined by a colorimetric assay. Finally, acetyl-cholinesterase (AChE) activity was measured in the absence and presence of IRCM. Results: High concentrations (>50 mM) of IRCM inhibited O₂ - production, ionic more than non-ionic IRCM. Medium concentrations (25-50 mM) of IRCM reduced OH production, and both types of IRCM were equally potent. Low concentrations (<25 mM) of non-ionic IRCM displayed higher antioxidant capacity than their ionic counterparts when tested in the TAS assay. Visipaque 320 (iodixanol) was found thave the highest TAS value, followed by Omnipaque 350 (iohexol), Hexabrix 320 (ioxaglate), and Urografin 370 (diatrizoate). Conclusion: IRCM have in vitrantioxidant properties in concentrations relevant for their clinical application. These properties may therefore be of potential importance when evaluating IRCM effects in vivo, particularly those concerning cardiovascular and renal function