Gadodiamide injection, a new nonionic, MRI contrast medium, was compared with the ionic agent gadolinium (Gd)-DTPA at 0.1 mmol/kg body weight in a double-blind, randomised trial in 60 patients, 30 receiving each substance, with known or suspected lesions of the central nervous system. The patients were closely questioned about adverse events. In the Gadodiamide injection group, four patients reported six adverse advents, three of which were judged to be related to the contrast medium. In the Gd-DTPA group, two patients each reported one adverse event, both of which had an uncertain relation to the contrast medium. All events were mild and no medical treatment was needed. No significant change in neurological findings, blood pressure, pulse rate or blood parameters were noted in any patient. Both contrast media were effective; no difference in overall efficacy or safety was observed.