Eighty-two patients with known or suspected multiple sclerosis (MS) were examined by means of magnetic resonance imaging (MRI) with a 0.15-T resistive scanner. The diagnosis could be made by MRI in 34 (97%) of the 35 patients with chronic, well-documented, stable MS and by high-volume delayed x-ray computed tomography (HVD CT) in only 6 (54%) of 11 patients in this group. The stage of the disease as judged from the MRI scans correlated poorly with the clinical status of the patient and with the known duration of the disease. MRI identified 28 (88%) of the 32 patients in whom MS was subsequently diagnosed by a neurologist, whereas regular contrast or HVD CT identified only 11 (52%) of 21 such patients. MRI is the most sensitive imaging modality for MS but is of little value in assessing the severity of the disease: many of the lesions seen on MRI scans are clinically "silent", and MRI does not usually detect small lesions in the brainstem, cerebellum or spinal cord that may be clinically significant.