Interferon-β-1b (Betaseron®, Betaferon®) is a non-glycosylated recombinant human interferon-β approved for high-frequency, subcutaneous (SC) administration in the treatment of multiple sclerosis (MS). Its mechanism of action is unknown, but may involve modulation of the autoimmune pathogenic processes of MS.In a randomised, double-blind trial in patients with relapsing-remitting MS (RRMS), SC interferon-β-1b 250µg (8 million International Units [MIU]) every other day reduced the annual relapse rate and increased the proportion of relapse-free patients compared with placebo. It also reduced relapse severity, hospitalisations, and disease activity assessed by magnetic resonance imaging (MRI), and increased the time to first relapse. Progression of disability showed a trend towards reduction relative to placebo and baseline, but did not reach statistical significance.SC interferon-β-1b 250µg every other day was shown in a randomised trial to be superior to intramuscular (IM) interferon-β-1a 30µg (6 MIU) once weekly with respect to reductions in relapse-related parameters, disability progression and MRI-assessed disease activity.In patients with secondary progressive MS (SPMS), SC interferon-β-1b 250µg every other day slowed progression of the disease relative to placebo in one randomised, double-blind trial, but not in another. In both studies, interferon-β-1b 250µg recipients had fewer relapses and less MRI-assessed disease activity than placebo recipients. The difference in primary outcome may reflect differences in patient entry criteria.Interferon-β-1b is generally well tolerated and the common adverse events (e.g. injection site reactions, asthenia and an influenza-like symptom complex) are clinically manageable. In a randomised trial, the tolerability of SC interferon-β-1b 250µg every other day was generally similar to that of IM interferon-β-1a 30µg once weekly, except for higher incidences of injection site reactions and neutralising anti-interferon-β antibodies with SC interferon-β-1b.In conclusion, SC interferon-β-1b 250µg every other day reduces the frequency and severity of relapses and MRI measures of disease activity and may delay the progression of disability in RRMS. The drug appeared to be more effective than, and as well tolerated as, IM interferon-β-1a 30µg once weekly. Interferon-β-1b also has positive effects on relapse rates and disease activity in patients with SPMS, although its effects on disease progression remain uncertain. The drug is generally well tolerated, and the common adverse events are clinically manageable. Thus, interferon-β-1b is a valuable first-line therapy for patients with RRMS and a potentially useful option in those with SPMS.