Tumor necrosis factor (TNF)- is a potent inducer of apoptotic cell death in various tissues, whereas the transcription factor nuclear factor (NF)-B is essential to protect against TNF--induced apoptosis. Human hepatoma cell lines were used to investigate the effectiveness and specificity of the fungal metabolite gliotoxin in inhibiting TNF--induced NF-B activation in transformed cells. Gliotoxin-TNF- cotreatment induced massive apoptosis in these otherwise TNF--resistant cell lines. With the use of the mouse partial hepatectomy model, we were also able to demonstrate in vivo the capacity of gliotoxin to act as inhibitor of NF-B activation. Bromodeoxyuridine staining of liver sections showed that the lack of NF-B activation correlated with 80% reduction of DNA synthesis 48 h after hepatectomy compared with untreated controls. Additionally, animals treated with gliotoxin showed nuclear condensation and DNA laddering of hepatocytes indicative of apoptosis 24 h after hepatectomy. In summary, our results demonstrate that NF-B is essential in defining the fate of liver cells in response to TNF- in vivo and furthermore implicate gliotoxin as a potential new response modifier for TNF--based therapy.