A number of autoantibodies play a significant role in collagen vascular diseases and represent diagnostic markers of some of these entities. Despite increasing knowledge of these serological findings, data are limited about potential disturbances of precursor cells that finally lead to the autoantibody producing plasma cells. Recent evidence of disturbed B cell homeostasis indicates that the peripheral B cell compartments in systemic lupus erythematodes (SLE) and Sjögren's syndrome are characteristically different to normal. Although the identification of autoreactive B cells in peripheral blood is still subject of ongoing studies, the differences in B cell subsets add to the understanding of the immunopathogenesis of these diseases and may provide new diagnostic clues and therapeutical avenues of these entities.