We report here that transforming growth factor-β1 induces cell death in the Morris hepatoma cell line McA-RH7777. We assessed the type of cell death induced by transforming growth factor-β1 in this hepatoma cell line on the basis of morphological and biochemical characteristics. Dying cells, which detached from the cell monolayer, showed morphological characteristics of apoptosis (programmed cell death) such as chromatin condensation, nuclear disintegration and cellular fragmentation into clusters of eosinophilic globules. DNA isolated from these cells showed a ladder pattern consisting of multimers of 180 to 190 bp, indicating extensive DNA cleavage into oligonucleosomal units by an endogenous endonuclease. Treatment of the dead cells with detergents and chaotropic agents resulted in formation of insoluble shells, so-called apoptotic bodies, suggesting extensive cross-linking of cell proteins by tissue transglutaminase. Furthermore, increased amounts of cytosolic tissue transglutaminase, which has been recognized as a possible marker of apoptosis, and extensive crosslinking of cytokeratin polypeptides was demonstrated in TGF-β1-treated hepatoma cells on immunoblot analysis. These results provide strong evidence that the cell death induced by TGF-β1 in McA-RH7777 hepatoma cells is mainly apoptotic. It also suggests that a specific induction of the cytosolic tissue transglutaminase may be involved in the TGF-β1-induced pathways of apoptotic cell death in McA-RH7777 hepatoma cells. (HEPATOLOGY 1993;18:945-953).