Three previously selected monoclonal antibodies (mAb) directed against the clonotypic structure of a variant (termed JA3) of the interleukin 2 (IL-2)-producing Jurkat leukemia cell line (anti-JTi1-3 mAb) were found to induce an adherent cell-dependent proliferation of peripheral blood T cells in 20 different donors. Unlike the early cell proliferation induced by anti-T3 mAb, anti-JTi mAb-induced proliferation was detectable at day 5-6 of culture and reached peak levels at day 7-9. Less than 1% JTi+ cells were consistently detected in the starting peripheral blood lymphocytes or in control cultures in which cells were stimulated with anti-T3, phytohemagglutinin, or allogeneic cells. However, JTi+ cells were found in increasing proportions after culture with anti-JTi mAb and they were mostly represented by large blast cells expressing either the T4 or the T8 antigen, together with typical activation antigens including HLA-DR, IL-2 receptor, and 4F2. Immunoprecipitation experiments and sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that anti-JTi-reactive molecules present on antibody-stimulated lymphocytes or on JA3 cells were similar, disulphide-linked heterodimeric structures.