['The aims of this study were to measure the levels of interleukin (IL)-33 and ST2 and T-helper (Th)2-associated cytokines (IL-13, IL-4, IL-5) in patients with ankylosing spondylitis (AS), and examine the correlation of serum cytokine levels with disease activity and laboratory parameters.', 'Serum IL-33, IL-13, IL-4, and IL-5 levels were assessed by sandwich enzyme-linked immunosorbent assay (ELISA), and the mRNA levels of IL-33 and ST2 were quantified by real-time quantitative polymerase chain reaction (RT-qPCR), in 43 AS samples and compared with 27 age- and sex-matched healthy controls.', 'Serum IL-33, IL-13, and IL-4 levels were increased significantly in AS patients compared with controls (p < 0.01); moreover, serum IL-33 and IL-13 levels were significantly higher in patients with active AS than in those with inactive AS (p < 0.05). The serum levels of IL-5 showed no significant difference between AS patients and controls (p > 0.05). Serum IL-33 levels were positively correlated with both IL-13 (r = 0.306, p < 0.01) and IL-4 levels (r = 0.432, p < 0.01). The mRNA levels of IL-33 and ST2 were significantly different between AS patients and controls (p < 0.01) but not between active and inactive AS patients.'] Are serum levels of IL-33 and its receptor ST2 elevated in patients with ankylosing spondylitis?