6 minutes after Joduron | 70% (0.5 ml/kg), Biligrafin | 30% (0.4 ml/kg), Urografin | 60% (0.5 ml/kg), Urovison | 58% (0.5 ml/kg), Urovist | 65% (0.75 ml/kg) and Conray | 70% (0.5 ml/kg) (within 1 minute injected) the level of circulating histamine in plasma is increased from less than 1.0 ng/ml to 2.0-2.5 ng/ml. The elevated levels return to normal within 20 minutes, in the case of Joduron | 70% and Biligrafin | 30% slower than after the other contrast media. Urivison | 30%, infused over 4 minutes (total dose 4 ml/kg), as dextrose 50%-solution (0.5 ml/kg) failed to change histamine concentration in plasma. Obviously the histamine liberating effect of the contrast media is a specific effect of these agents.