A group of 21 patients with clinically confirmed multiple sclerosis were treated for one year with azathioprine, Germed, in daily doses of 50 or 75 mg depending on body weight. After two months the treatment was stopped for one month. The control group received prednisone (Encorton, Polfa) 5 or 10 mg daily. The drugs were given in wafers in powdered form. The double blind method was used. After one year the comparison of both groups failed to show any significant differences, and the reduction in the indices of exacerbations and stabilization of the process evaluated by Kurtzke's scale were nearly identical. However, this might have been due to the fact that nearly one-third of the patients dropped out from both groups. During the treatment with azathioprine no significant differences were noted in the surface phenotypes of peripheral blood mononuclear cells.