Ioversol 300 (Optiray 300) is a new low-osmolality contrast medium. Optiray 300 was used in 92 patients for CT examination of the brain, to assess its clinical tolerance. Adverse reactions, when sensations of heat were neglected, were observed in 15% of the patients. All the adverse reactions, either observed by the radiologist or pointed out by the patient, have spontaneously disappeared without medical treatment and did not require hospitalization. Anaphylactoid phenomena were not observed. Optiray 300 appears as a well suited contrast medium for CT scan of the brain especially in patients with contrast medium high risk.