In a longitudinal prospective study, we followed 56 patients (17 men, 29 women) with definite multiple sclerosis (MS), who were treated with high-dose intravenous methylprednisolone (IVMP), 10 consecutive days with 1000 mg IVMP daily. Mean follow-up period after entry was 2.6 years (range 1.7-3.5 yrs). All patients were treated because of a symptomatic deterioration. Independent of the disease courses (RR-relapsing remitting/CP-chronic progressive/CP+RR- mixed course), 65% of the 46 MS patients (30/46) showed a clinical improvement after the first IVMP course, expressed by a decrease in the EDSS rating (1.0 point or more). During the follow-up period 59 additional IVMP courses (range 0-5 courses per patient) were given; 8 patients were treated with a combination of cyclophosphamide and prednisone, because of strong continuous progression. During the follow-up period 19 patients (41%) showed an increase in the EDSS-rating (1.0 point or more) compared with the EDSS level just after the first IVMP; 22 patients (48%) had no changes in the EDSS-rating, and 5 patients (11%) showed a clinical improvement (decrease of 1.0 point or more). In the relapsing MS patients (RR and CP+RR, n = 38) mean relapse rate/patient/year prior to the first IVMP was 2.6, which significantly (p < 0.0001) decreased to 0.8 during the follow-up period. Statistically no significant difference was found between baseline EDSS and EDSS ratings after the follow-up period in relapsing MS patients.(ABSTRACT TRUNCATED AT 250 WORDS)