The discomfort of cerebral arteriography is due mainly to the osmolality of the contrast medium injection. A new low osmolality contrast medium--Hexabrix (32% iodine)--sodium and meglumine salts of ioxaglic acid was compared with Conray 280 (28% iodine)--meglumine iothalamate for carotid arteriography in 33 conscious patients. 30 patients preferred the ioxaglate solution which caused significantly less sensation of heat. Three patients could not distinguish between the two media. No patient preferred iothalamate. Ioxaglic acid is a newly synthesized mono-acid dimer. Its salts produce the same osmolality as non-ionics (e.g. metrizamide), and one third of the osmolality of currently used mono-valent salts (e.g. meglumine iothalamate) in solutions of the same iodine content. Low osmolality contrast media have significant clinical advantages and will probably become the media of choice for arteriography and venography.