Information obtained from CT scan after contrast administration was evaluated in 59 consecutive stroke patients. CT scans before and after contrast administration were performed 3 days and 2 1/2 weeks after stroke. A plain CT scan was repeated 6 months later. Contrast enhancement was practically not seen on the first examination, but was seen in 46% on the second examination. There was a close relationship between the occurrence of contrast enhancement and the socalled "fogging effect". Contrast scanning gave additional information only when this effect was present. Plain CT scans 3 days after stroke were superior to contrast scans taken at any time for detecting and visualizing cerebral infarcts.