Twenty-six acute exacerbations in 26 patients with early definite multiple sclerosis (MS) were treated with oral cyclosporin-A (CyA) or oral prednisolone in a double-blind, controlled and randomized trial. The duration of the treatment was 6 weeks. All of the patients showed improvement during the treatment. There were no differences in outcome between patients on CyA (7.5 mg/kg) or prednisolone (decreasing doses from 0.8 mg/kg) during the 6 week treatment. However, the improvement of clinical signs 3 months after the treatment was slightly greater in the prednisolone group. The drugs did not have significant side-effects. There was no fluctuation in the CD4/CD8 ratio during the follow-up. The two treatment groups did not differ from each other in respect to the number of CD3 (T3), CD4 (T4), CD8 (T8), CD14 (monocytes), CD20 (B cells) or CD25 (interleukin-2 receptor positive cells). The number of active T cells with the interleukin-2 receptor was high in the beginning of the exacerbation but it decreased during the treatment. To conclude, the effects of CyA and prednisolone were comparable in the treatment of acute MS relapses.