The highly effective treatment of rheumatoid arthritis by B cell depletion and the presence of B cells in the peripheral and axial lesions of patients with spondylarthritis (SpA) raise the question as to whether B lymphocytes could also be an appropriate therapeutic target in the latter disease. We describe 2 male HLA–B27–positive patients who had active SpA despite absence of B cells. One patient developed SpA with sacroiliitis and asymmetric oligoarthritis after having been diagnosed as having severe Bruton agammaglobulinemia. Since extensive investigations excluded an infectious origin of the SpA, this case illustrates that functional B cells and/or gamma globulins are not strictly required for SpA pathogenesis. The second patient had severe axial and peripheral SpA that was treated successfully with etanercept. After discontinuation of etanercept treatment because of non-Hodgkin's B cell lymphoma, both axial and peripheral SpA symptoms relapsed rapidly, and this exacerbation of articular disease activity was not modulated by successful B cell depletion therapy for the lymphoma. Although case reports have obvious limitations, our clinical observations provide evidence that active SpA can occur in the absence of functional mature B cells and thus emphasize the need for systematic studies of the exact role and function of B lymphocytes in this disease.