The objectives of the study are:

- comparison of the incidence and time course of the development of neutralizing antibodies (NAbs) to Rebif after 48 weeks of therapy, to historical data from Serono clinical trial databases to assess the safety and tolerability of Rebif®

Inclusion Criteria:

• Have multiple sclerosis (MS) with two or more relapses in the past two years and is eligible for interferon therapy.

• Be between 18 and 60 years of age, inclusive.

• Have given written informed consent, prior to any study related procedure not part of normal medical care, with the understanding that consent may be withdrawn by the subject at any time without prejudice to their future medical care.

• Be willing and able to follow all study procedures for the duration of the study.

• Have an Expanded Disability Scale Score (EDSS) less than 6.0

• If female, she must either

  1. be post menopausal or surgically sterilised; or
  2. use a hormonal contraceptive, intra uterine device, diaphragm with spermicide, or condom with spermicide, for the duration of the study; and
  3. be neither pregnant nor breast feeding. Confirmation that the subject is not pregnant must be established by a negative SERUM human Chorionic Gonadotrophin (hCG) pregnancy test between 28 to 7 days before Study Day 0.Urine pregnancy test must be done if serum hCG pregnancy test was performed more than 7 days before Study Day 0. A pregnancy test is not required if the subject is post menopausal or surgically sterilised.

Exclusion Criteria:

• Prior Interferon beta therapy (either beta-1b or beta-1a).
• Major medical or psychiatric illness that in the opinion of the investigator creates undue risk to the subject or could affect compliance with the study protocol.
• Significant immunosuppressive therapy within the 6 months prior to enrolment.
• Known history of hypersensitivity to natural or recombinant interferon beta, human serum albumin, or any other component of the formulation.
• Epilepsy with a history of seizures not adequately controlled by treatment.
• Have greater than Grade 1 toxicity for liver function tests (Aspartate Transaminase (AST), Alanine Transaminase (ALT), Gamma-Glutamyl Transferase (GGT) or total bilirubin) at the Screening visit
• Have significant leukopenia (greater than Grade 1 toxicity for total white blood cell count or lymphopenia) at the Screening visit
• Have had treatment with oral or systemic corticosteroids or Adrenocorticotrophic hormone (ACTH) within 1 month of the Screening visit or between the screening visit and study day 0.
• Cytokine or anti-cytokine therapy within the 3 months prior to the Screening visit or between the screening visit and study day 0.
• Use of immunomodulatory or immunosuppressive therapy (including but not limited to cyclophosphamide, cyclosporin, methotrexate, azathioprine, linomide) within the 6 months prior to the Screening visit or between the screening visit and study day 0.
• Have taken intravenous immunoglobulin or glatiramer acetate or mitoxantrone or any investigational drug or experimental procedure within the 3 months prior to the Screening visit or between the screening visit and study day 0.
• Prior use of cladribine or have received total lymphoid irradiation.
• Presence of systemic disease that might interfere with patient safety, compliance or evaluation of the condition under study (e.g. poorly controlled insulin-dependent diabetes, Lyme disease, clinically significant cardiac disease, human immunodeficiency virus (HIV), human T-lymphotrophic virus 1 (HTLV-1)).

Other concurrent systemic disorders incompatible with the study (at the Investigator's discretion).

48 weeks

Comprehensive assessments of any apparent toxicity experienced by the subject were performed throughout the course of the study. Study site personnel reported any AE, whether observed by the Investigator or reported by the subject.