TGF-β a pleiotropic, peptide growth factor has usually been associated with the initiation of apoptosis. We have shown in three human tumor cell lines, using acridine orange staining and fluorescent microscopy, that TGF-β can protect cells from, the onset of Fas initiated apoptosis. This protection is apparently not associated with growth inhibition or cell adhesion. We have investigated whether the down regulation of c-myc. a known activity of TGFβ, could be responsible for this protection.