Recently, we showed that TNF enhances the susceptibility of endothelial cells from murine liver sinusoids (LEC) to Fas-mediated apoptosis, suggesting that signals transduced by Fas and TNF receptors may synergistically increase intracellular death signals in these cells. In this work we evaluated whether caspase-3 and p38 are involved in LEC apoptosis induced by Fas and TNF. Here we show that LEC treated with Fas agonist (Jo2 mAb at 0.1 microg/ml) and TNF had a greater caspase-3 activity (twofold increase) than cells treated with each factor alone. There was a strong correlation between caspase-3 activity and cell killing induced by Jo2/TNF, indicating that this caspase plays a critical role in this process. Likewise, there was a significant increase in caspase-8 activity in LEC treated with Jo2 and TNF, compared with untreated cells or cells treated with each factor alone. Apoptosis of LEC induced by Jo2/TNF was partially reversed by SB203580, a p38 inhibitor, suggesting that p38 is involved in apoptosis of these cells. To our knowledge, this is the first report that apoptosis induced by Fas/TNF in LEC is associated with coactivation of both caspase-3 and p38. Potentially, both caspase-3 and p38 may be of great importance in endothelial cell pathology as molecular targets for preventing vascular damage due to endothelial cell apoptosis.