Antigen-specific T cell tolerance can be induced by systemic injection of high-dose antigen. In particular, a single intravenous (i.v.) injection of influenza virus hemagglutinin peptide in HNT-TCR transgenic mice induces T cell tolerance through thymocyte apoptosis as well as anergy and deletion of peripheral CD4+ T cells. We now show that this tolerance is reversed after 8 weeks probably due to the short in vivo half-life of the peptide. Since durable tolerance is required for this strategy to be of therapeutic value, we tested whether weekly i.v. injections of peptide (up to 12 weeks) could maintain the CD4+ T cell tolerance. Each injection induces a profound deletion of thymocytes, although their level recovers before the next injection. Therefore, during the treatment period, the thymus undergoes cycles of contraction/expansion. In the periphery, the number of CD4+ T cells is stably decreased and the persisting CD4+ T cells are hyporeactive both in vitro and in vivo. This tolerance is essentially peripheral since comparable results were obtained in thymectomized HNT-TCR mice injected weekly. Our data show that stable antigen-specific tolerance can be induced by repeated i.v. injections of antigen. These findings might have implications for the treatment of T cell-mediated autoimmune diseases.