An ELISA test was performed in order to measure the serum levels of secretory IgA (sIgA) in 51 patients with ankylosing spondylitis (AS) and 30 healthy controls. Raised values of sIgA were found in AS patients compared to controls. Patients with active disease, defined by clinical criteria, showed a significant elevation of serum sIgA compared to healthy controls (p = 0.03) or to patients with inactive disease (p = 0.02). A positive correlation between total serum IgA and sIgA was found (p = 0.001). Our findings further support the role of the mucosal stimulation in the pathogenesis of AS.