Clinical aspects of dendritic cells have yet to be studied intensively. One obstacle, that of isolating and identifying dendritic cells from human blood and other tissues like skin and tonsil, is being overcome, although the field would be facilitated by dendritic-cell-specific monoclonals or other probes. Many of the specializations that dendritic cells exhibit as antigen-presenting cells in other mammals are being verified in man. New properties, particularly their capacity to induce clonal expansion of T cells and to be infected with retroviruses, have become evident. Four areas where it may be productive to give more attention to dendritic cells are transplantation, protective T-cell immunity, autoimmunity and HIV-1 infection.