Activation of lymphocytes in the presence of transforming growth factor beta (TGFbeta) can impair or enhance their functional activity. We have found that TGFbeta is important in the generation of lymphocytes, which are capable of suppressing antibody production. To better understand how this cytokine affects lymphocyte activity, we looked at the expression of early activation events of T cells stimulated in the presence or absence of TGFbeta. The results show that TGFbeta enhances the expression of CD154 (CD40L), TNFR2 and the production of TNFalpha. These findings clarify the co-stimulatory effects of TGFbeta that enhance T lymphocyte activation.