<qa>  What is the duration of the double-blinded treatment period?The purpose of this study is to assess the efficacy of oral methotrexate in adult subjects with active axial spondyloarthritis. Subjects will be randomly assigned to placebo or methotrexate treatment groups. All subjects in the active treatment group receive at least a dose of 15 mg per week of oral methotrexate. To reduce mucosal, gastrointestinal and haematologic side effects of low-dose methotrexate all study subjects receive also a dose of 5 mg per week of folic acid. A stable dose of NSAID during the study is permitted. The duration of the double-blinded treatment period is 24 weeks. 