In this study, efficacy of methylprednisolone in reduction of signs and symptoms (back pain, stiffness, joint pain and swelling) of active ankylosing spondylitis (AS) will be investigated. It is expected, that a single dose of methylprednisolone 500 mg given intravenously at baseline will lead to a rapid reduction of symptoms of active AS, which can be seen already 2 weeks after drug administration.

Inclusion Criteria:

• Age of ≥18 years.
• Definite diagnosis of AS according to the modified New York criteria.
• History of an inadequate response to ≥2 nonsteroidal antiinflammatory drugs (NSAIDs) taken for at least 2 weeks each or NSAIDs intolerance.
• Active disease as defined by the Bath Ankylosing Spondylitis DIsease Activity Index (BASDAI) value of ≥4 at screening despite concomitant treatment with an NSAID or without NSAIDs in case of intolerance.

Exclusion Criteria:

• The female subject is pregnant or lactating.
• Patients with other chronic inflammatory articular disease or systemic autoimmune disease.
• History of inadequate response to previous anti-tumour necrosis factor (TNF) α therapy.
• Treatment with any other investigational drug within 4 weeks of 5 half-life of the drug (whichever is longer) prior to baseline.
• Treatments with disease modifying anti-rheumatic drugs (DMARDs) other than methotrexate within 4 weeks prior to screening (8 weeks for leflunomide or 4 weeks with a standard cholestyramine wash-out).
• Treatment with intravenous, intramuscular or intraarticular/periarticular steroids within 4 weeks prior to screening.
• History of oesophageal, gastric, duodenal or intestinal ulceration, clinically relevant gastrointestinal bleeding.
• History of or current signs of coronary heart disease, myocardial infarction, stroke or transient ischemic attack, peripheral arterial thrombotic events.
• Congestive heart failure (NYHA III-IV)
• Uncontrolled arterial hypertension.
• History of diabetes mellitus.
• History of glaucoma.
• Major surgery within 12 weeks prior to screening.
• Evidence of any other severe uncontrolled gastrointestinal, hepatic, renal, pulmonary, cardiovascular, nervous or endocrine disorders.
• Any active current viral, bacterial or fungal infection, a history of recurrent clinically significant infection, infections requiring treatment with antibiotics within 4 weeks prior to baseline.
• History of chronic infection with hepatitis B or C, history of HIV infection.
• Primary or secondary immunodeficiency.
• Any other conditions making the patient unsuitable in the opinion of the investigator for the participation in the current study.