Several phase III studies have proven that the beta-interferons have positive effects on the number and severity of acute exacerbations of relapsing remitting multiple sclerosis. Recently the first study on the effectiveness of interferon beta-1b in secondary progressive multiple sclerosis was published. In a multicenter, double-blind, randomized, Placebo-controlled study 718 patients with secondary progressive multiple sclerosis and an expanded disability status scale (EDSS) value between 3.0 and 6.5 were treated with either 8 Mio.interferon beta-1b or Placebo subcutaneously every second day for two to three years. The primary study end-point was the time until confirmed progression of the disease as signified by a one point increase of the EDSS value (for initial EDSS values between 3.0 and 5.5) or 0.5 point increase when the initial EDSS value was between 6.0 and 6.5. After two years an interim analysis showed a highly significant difference in delay of disease progression by nine to twelve months for the treatment group (p = 0.0008). This means that interferon beta-1b is the first recombinant beta-interferon to be shown effective in the treatment of secondary progressive multiple sclerosis.