T-Cell hybridomas were constructed by fusing BW5147, an AKR lymphoma, with concanavalin A-stimulated murine splenic lymphocytes. The hybrids which were formed were studied for their ability to produce a lymphokine which inhibits tumor cell migration (TMIF) as well as macrophage migration (MIF) using in vitro assays. Clones were identified which affected tumor cell motility without exerting similar effects on murine macrophages, although the opposite effect was not observed. Although noncoordinate production of these factors cannot be unequivocally established, these results demonstrate that clones can be constructed that preferentially secrete TMIF. In these experiments, we also tested the supernatants for another lymphokine effect on tumor cells; namely, the ability to inhibit tumor cell binding to endothelial monolayers. A number of clones were identified that lacked TMIF activity, but could inhibit the tumor cell-endothelial interaction, suggesting the possibility that these effects may be due to separate mediators.