Immunologic tolerance is a state of immune paralysis specific to a given antigen (the tolerogen) coexisting with the maintenance of normal immunocompetence towards other antigens. Anti-T cell monoclonal antibodies allow its induction in organ transplantation and autoimmune disease essentially through the stimulation of regulatory T cells. Very promising results obtained in animals have been recently confirmed in the human in recent-onset insulin-dependent diabetes mellitus with an anti-CD3 antibody (with long-term remission of the disease following a treatment of only six days).