The study is conducted in order to find out if repeated doses of the monoclonal (artificially manufactured) antibody BT061 can help arthritis patients whose disease does not sufficiently respond to a treatment with methotrexate (MTX).

Patients showing active rheumatoid arthritis according to ACR criteria despite at least 6 months of treatment with methotrexate fulfilling all other inclusion criteria including written informed consent and none of the exclusion criteria (see below) have the opportunity to be randomised to either treatment with BT061 or placebo, both given subcutaneously in a double-blind set-up.

Inclusion Criteria:

• Patients with active Rheumatoid Arthritis (RA) according to 1987 revised ACR criteria with functional class II-III
• Disease activity at screening and baseline (more than 6 swollen joint count; more than 6 tender joint count; elevat. of CRP or ESR)
• Duration of RA more than 12 month
• History of at least one disease-modifying anti-rheumatic drug (DMARD) with an inadequate response despite more than 3 month of treatment
• MTX treatment at least 6 month with a stable dose at least 15mg MTX
• Patients could continue at more than daily 7,5mg of prednisone or equivalent stable dose at least 6 weeks prior baseline
• Written Informed Consent

Exclusion Criteria:

• Treatment with traditional DMARDs apart from MTX 12 weeks prior to baseline and DMARD leflunomide 24 weeks
• Treatment with any biologics other than TNF-α inhibitors (e.g. abatacept, rituximab, tocilizumab, anakinra)
• treatment with any TNF-α inhibitor within 5 elimination half-lives prior baseline and during the study
• Clinical non-response to more than one of TNF-α inhibitor exceeding adequate treatment duration