The influence of aortic arch injection of metrizoate 280 and 370 mg I/ml and ioxaglate 280 and 320 mg I/ml on EEG, heart rate, blood pressure, subjective responses, occurrence of involuntary movements and resulting image quality was investigated in 31 patients. Ioxaglate 320 produced less haemodynamic changes and subjective responses and as good image quality as the hyperosmolar contrast medium metrizoate 370 if subtraction procedure was used. Small and brief EEG changes were recorded in 9 of 14 patients. Only metrizoate 280 induced significant bradycardia. Involuntary movements on the film with the best demonstration of the vessels occurred with no difference between the contrast media. There was no correlation between involuntary movements and image quality. Our investigation indicates that an ionic contrast medium which is intended for aortocervical angiography should have a concentration of at least 320 mg I/ml, high viscosity, low osmolality and be no pure meglumine salt.