Current ideas concerning various aspects of the biology of dendritic cells (DC) were presented, including subdivision on two subsets and follow-ups of their activation. The issue of DC cross-presenta- tion (cross-priming) was discussed in detail as an important facet of their immunobiological function. The relevant role of DC in immunoregulation was underlined, particularly the action of immunosuppressive cytokines such as IL-10 and TGF-β and the enzyme indoleamine 2,3-dioxygenase (IDO). Attention was paid to the significance of DC in the induction of immunological tolerance.