In a prospective multicentre study of 4,970 contrast enhanced CT's with intravenous application of lohexol, no contrast medium induced side effects could be diagnosed in 98.4% of the patients. Patients with a positive history of allergic diathesis had an increased risk of unexpected contrast-medium induced systemic reactions (factor 2 to 3). In 21% the diagnosis could not be established by non-enhanced CT alone, whereas in 56% the diagnostic accuracy was improved by intravenous contrast medium injection.