The magnetic resonance imaging (MRI) characteristics of the apparently normal cerebral white matter were studied in a group of 35 patients with clinically definite multiple sclerosis (MS). The proton relaxation times were compared with those in normal control subjects and patients with clinically isolated neurologic lesions of a type common in MS. Significant differences were found between all the patient groups and the control subjects. Changes in the cerebral white matter may be an early feature of MS.