The goals of this protocol are to study the pathophysiology of multiple sclerosis (MS), primarily through small studies that utilize magnetic resonance imaging (MRI), and to correlate the results with clinical and biological measures. The protocol includes only techniques with minimal risk (standard and quantitative clinical evaluation, MRI, blood draws, saliva testing, urine and stool collection, lumbar punctures, visual evoked potentials, ophthalmologic evaluation) or more-than-minimal risk (injection of approved gadolinium-based contrast agents) that are appropriate and common in this study population. Under this protocol, we will conduct: