Induction of immunity and peripheral tolerance requires contacts between antigen-bearing dendritic cells (DCs) and cognate T cells. Using real-time two-photon microscopy, we have analyzed the dynamics of CD8(+) T cells in lymph nodes during the induction of antigen-specific immunity or tolerance. At 15-20 h after the induction of immunity, T cells stopped moving and established prolonged interactions with DCs. In tolerogenic conditions, despite effective initial T cell activation and proliferation, naive T cells remained motile and established serial brief contacts with multiple DCs. Thus, stable DC-T cell interactions occur during the induction of priming, whereas brief contacts may contribute to the induction of T cell tolerance.