These Proceedings contain the contributions of the partIcIpants of the Third International Symposium on Dendritic Cells that was held in Annecy, France, from June 19 to June 24, 1994. This symposium represented a follow-up of the first and second international symposia that were held in Japan in 1990 and in the Netherlands in 1992. Dendritic cells are antigen-presenting cells, and are found in all tissues and organs of the body. They can be classified into: (1) interstitial dendritic cells of the heart, kidney, gut, and lung;(2) Langerhans cells in the skin and mucous membranes; (3) interdigitating dendritic cells in the thymic medulla and secondary lymphoid tissue; and (4) blood dendritic cells and lymph dendritic cells (veiled cells). Although dendritic cells in each of these compartments are all CD45+ leukocytes that arise from the bone marrow, they may exhibit differences that relate to maturation state and microenvironment. Dendritic cells are specialized antigen-presenting cells for T lymphocytes: they process and present antigens efficiently in situ, and stimulate responses from naive and memory T cells in the paracortical area of secondary lymphoid organs. Recent evidence also demonstrates their role in induction of tolerance. By contrast, the primary and secondary B-cell follicles contain follicular dendritic cells that trap and retain intact antigen as immune complexes for long periods of time. The origin of follicular dendritic cells is not clear, but most investigators believe that these cells are not leukocytes.