A double-blind, placebo-controlled, randomized crossover trial of high-dose methylprednisolone (MP) was performed in 35 patients with a primarily chronic progressive form of multiple sclerosis as defined clinically according to Poser’s criteria. At time 0 of every course of treatment (1 g MP administered i.v. daily for 5 days followed by oral prednisone tapering over 4 days, or placebo) and at 10, 30 and 90 days thereafter, each patient underwent psychometric tests and was clinically tested according to Kurtzke’s Expanded Disability Status Scale (EDSS). The disability pattern of most patients who were treated with placebo either worsened or did not change. A statistically significant improvement (p < 0.001) of EDSS in MP-treated patients was recorded. The improvement mainly concerned the pyramidal, cerebellar and sensitive disorders; it was already evident at the first clinical follow-up and lasted for 3 months from the beginning of the treatment. No frequent and/or important side effects were detected throughout the tr