One of the important functions of granulocytes is the ability to respond to a chemoattractive signal by migration. The influence of radiographic contrast media (CM) on the chemoattractive properties of serum was investigated by under agarose technique for chemotaxis. No chemotactic response was seen when serum was incubated with different concentrations of CM after heat inactivation. The CM did not generate the heat stable complement split product C5a-desarg which would have resulted in a chemotactic response. Without heat inactivation all complement available in the serum was activated by the agarose in the chemotaxis assay. Low concentrations of iohexol and iodixanol brought about an increased chemotactic response relative to a reference with saline instead of CM. This may be due to activation of heat labile chemoattractants from other sources than the complement cascade. At high concentrations of all five investigated CM, a decreased number of granulocytes migrated over a shorter distance when compared with the reference, and this may be due to interactions between the CM and chemoattractants or their precursors.