In order to identify cell surface structures involved in the activation and growth of human-cloned T lymphocytes, we developed monoclonal antibodies against an autoreactive TcR gamma delta-bearing clone termed DS6. Antibodies were screened for their agonistic properties with the immunizing T cell clone. In the present report, we describe a CD30 mAb, termed BY88, that was capable of inducing, in a short-term assay, a strong proliferation of the T cell clone DS6 when added in combination with IL2 or phorbol myristate acetate. More important was the finding that in the total absence of feeder cells, BY88 mAb and recombinant IL2 were capable of maintaining long-term growth of DS6 cells. As this finding could not be extended to alloreactive cloned T lymphocytes, it is suggested that activation of T lymphocytes through the CD30 molecule is restricted to a T cell subset including autoreactive TCR gamma delta-bearing lymphocytes.