The purpose of this study is to compare efficacy, pharmacokinetics, and safety of investigational formulations of etanercept administered as 50 mg once weekly with 25 mg twice weekly and placebo in patients with ankylosing spondylitis (AS).

Inclusion Criteria:

• Diagnosis of AS, as defined by Modified New York Criteria for Ankylosing Spondylitis.
• Active AS, defined by average of visual analog scale (VAS) of ≥ 30 for duration and intensity of morning stiffness and at least 2 of the following: VAS for patient global assessment ≥ 30; average of VAS for nocturnal and total pain ≥ 30; BASFI ≥ 30 (all scores on a scale of 0 to 100).

Exclusion Criteria:

• Complete ankylosis (fusion) of spine.
• Previous treatment with etanercept, antibody to Tumor Necrosis Factor α (TNFα), or other TNFα inhibitors or other biologic agents.
• Use of disease modifying antirheumatic drugs (DMARDs) other than hydroxychloroquine, sulphasalazine, and methotrexate within 4 weeks of baseline. Subjects treated with hydroxychloroquine, sulphasalazine, and methotrexate may continue these drugs during this study but doses must be held stable for 4 weeks before baseline examination and for the duration of the study.
• Receipt of multiple nonsteroidal anti-inflammatory drugs (NSAIDs) at baseline.
• Dose of NSAID changed within 2 weeks of baseline evaluation.
• Dose of prednisone >10 mg/day (or equivalent) or changed within 2 weeks of baseline evaluation.