Inclusion Criteria:

- Adult patients ≥ 18 years of age.

- Ankylosing spondylitis as defined by the modified New York criteria for ≥ 3 months
prior to baseline.

- Active disease at screening and baseline (Bath Ankylosing Spondylitis Disease
Activity Index [BASDAI] ≥ 4.0, spinal pain visual analog scale [VAS] ≥ 40).

- Inadequate response or intolerant to 1 or more previous non-steroidal
anti-inflammatory drugs (NSAIDs).

- Inadequate response to treatment with etanercept, infliximab, adalimumab, or
golimumab because of inadequate efficacy.

- Tumor necrosis factor (TNF) antagonist therapy must have been discontinued at least 8
weeks prior to baseline (etanercept 4 weeks).

- Traditional disease-modifying anti-rheumatic drugs (DMARDs) must be withdrawn for at
least 4 weeks prior to baseline (methotrexate, sulfasalazine, and hydroxychloroquine
or chloroquine may be allowed if at stable dose for at least 4 weeks prior to
baseline).

- Oral corticosteroids (≥ 10 mg/day prednisone or equivalent) and
NSAIDs/cyclooxygenase-2 [COX-2] inhibitors must be at stable dose for at least 4
weeks prior to baseline.

Exclusion Criteria:

- Major surgery (including joint surgery) within 8 weeks prior to screening or planned
major surgery within 6 months after randomization.

- Total ankylosis of spine (as determined by investigator).

- Inflammatory rheumatic disease other than ankylosing spondylitis.

- Active, acute uveitis at baseline.

- Previous treatment with tocilizumab.

- Intra-articular or tendon injections or parenteral corticosteroids within 4 weeks
prior to screening.

- History of severe allergic or anaphylactic reactions to humanized or murine
monoclonal antibodies.

- Active current or history of recurrent bacterial, viral, fungal, mycobacterial, or
other infection.

- History of or currently active primary or secondary immunodeficiency.

- Body weight > 150 kg.