MRI of twenty patients with cerebral infarction were reported with their X-CT. MRI with long SE mode clearly showed the ischemic lesion at 18 hours after insult, whereas X-CT performed immediately after MRI scanning showed no abnormality. The signal contrast of the lesion with long SE mode seemed to increase slightly during the patient's course, for a period of several months. The MRI images with long SE at the chronic stage were varied: small lesions appeared as hot areas, whereas large lesions appeared as cold areas and were accompanied with signal enhancement in the surrounding areas. A phantom study was also performed and it was determined that MRI was superior to X-CT in its ability to detect tissue water. One of the reasons for the high diagnostic capability of MRI for acute stroke was, therefore, attributed to this experimental result.