This is an open-label, Phase III study to evaluate the efficacy, safety and PK of MRA in patients with pJIA.

Inclusion criteria

• Patients who are diagnosed with rheumatoid factor (RF) positive or negative polyarthritic or oligoarthritic JIA according to the ILAR standards (1997)
• Patients aged at least 2 years old and less than 20.
• Patients aged less than 16 years old at time of onset

Exclusion criteria

• Patients with Class IV Steinbrocker functional disorder at evaluation within 2 weeks before initiation of treatment with the investigational product
• Patients who have been treated for the underlying disease with a biological agent, such as infliximab or etanercept, within 12 weeks before initiation of treatment with the investigational product