Follicular dendritic cells (FDCs) have important functions in the selection of memory B lymphocytes during germinal center reactions (GCR). They present native antigens to potential memory cells, of which only B cells with high affinity B cell receptors (BCR) can bind. These B lymphocytes survive, whereas nonbinding B cells undergo apoptotic cell death. FDCs are present in follicles of any secondary lymphoid organ and belong to the stromal cells of these organs. Ectopic FDC-formation can be found in a number of autoimmune diseases and/or chronic inflammatory situations. This indicates that the development of FDCs is not restricted to secondary lymphoid organs, but that it is rather a matter of local conditions that drives a precursor cell type into FDC-maturation. A precursor of FDCs has presently not been identified, but phenotypic marker studies, in vitro experiments with fibroblast-like cell lines, and recent data on mesenchymal precursor cells from the peripheral blood suggest a close relation to fibroblast-like cells.