In a prospective study, we compared the number of gadolinium-DTPA (Gd-DTPA) enhancing lesions on MRI with the CSF and clinical findings before and after a total of 20 courses of high-dose intravenous methylprednisolone in relapsing multiple sclerosis patients. Before treatment, there was a significant correlation of Gd-DTPA enhancement (seen on 16 of 20 scans) and CSF myelin basic protein (MBP). If enhancement with Gd-DTPA represents inflammation and CSF-MBP indicates myelin breakdown, the amount of inflamed tissue should correlate with the amount of myelin being damaged. Clinical improvement occurred following 15 of 20 courses, and decrease of Gd-DTPA enhancement in 12 of 16 scans; the mean CSF-MBP level was the only CSF variable to return to reference values. There was a significant correlative triad of decrease in CSF-MBP, Gd-DTPA enhancement, and clinical disability. Thus, the clinical effect of methylprednisolone might be accompanied by a reduction of inflammation and myelin breakdown.