AbstractThe effects of radiographic contrast media (RCM) on leucocyte orientationin vitrowere studied using a Zigmond chamber. Leucocyte orientation was assessed following exposure of the leucocytes to iotrolan, iohexol, ioxaglate and diatrizoate. The RCM used were diluted to a concentration similar to that obtainedin vivoduring routine angiography. At this concentration there was a significant reduction in leucocyte orientation for all RCM investigated but the effect was more pronounced in the monomeric than the dimeric RCM. The results may have significance when deciding which radiographic contrast medium to use in selected patients, particularly those who are immunosuppressed or septicaemic.