Sepsis is associated with an increase in circulating levels of bacterial endotoxin. Sepsis is a particularly serious problem in the geriatric population due to the associated high mortality rate. However, it remains unknown whether this phenomenon is related to an increase in apoptosis in splenic cells. To investigate this issue, male Fischer-344 rats (young, 3 months old; aged, 24 months old) were subjected to endotoxemia by injection of LPS. Splenic samples were collected 4 h thereafter. Apoptosis was determined by cleaved caspase-3 levels and TUNEL staining. The levels of proinflammatory mediators, TNF-alpha, IL-6 and high mobility group box-1 (HMGB-1), were also measured. Our results showed that, while splenic cell apoptosis increased in the young and aged rats with endotoxemia, the aged animals had much higher levels of apoptotic cell death. The elevated expression of cell cycle inhibitory protein P21 was also observed in the aged animals after treatment with LPS. Moreover, endotoxemia significantly increased TNF-alpha, IL-6 and HMGB-1. The accelerated apoptosis in the aged animals was correlated with significantly higher levels of TNF-alpha, IL-6 and HMGB-1. It is suggested that this accelerated rate of apoptosis contributes to age-related hyperinflammation in endotoxemia. To investigate the factors involving accelerated apoptosis in aged animals, we analyzed the Fas/Fas ligand (Fas-L) pathway. Our results showed that Fas and Fas-L gene expression was markedly higher in the spleen in the aged animals after LPS. Similarly, cleaved caspase-8 expression, a downstream element of Fas and Fas-L, was also significantly higher in the aged rats after LPS. Fas-L neutralizing antibodies markedly decreased apoptosis and proinflammatory cytokines in the aged animals after endotoxemia. Thus, there is substantial evidence that the Fas/Fas-L pathway may play an important role in LPS-induced accelerated apoptosis and hyperinflammation in aged animals.