Wegener's granulomatosis (WG) and microscopic polyangiitis (MP) are "small vessel" vasculitides which can serologically be discriminated measuring autoantibodies directed towards different target antigens (ANCA). In the present study we can demonstrate increased autoimmunity in patients with MP, as evaluated by measurement of thyroid microsomal and cardiolipin antibodies. Neither thyroid microsomal- nor myeloperoxidase-, nor cardiolipin antibodies were correlated to each other.