Neutrophil apoptosis is delayed under trauma and/or sepsis injury conditions. The molecular mechanism for the delay in apoptosis has not been well defined. We investigated whether activation of PI-3 kinase/PKB signaling pathway contributes to the delay in neutrophil apoptosis with thermal injury. Rats were subjected to burns (30% total body surface area, 98°C for 10 sec), and euthanized 24 hours later. Blood neutrophils were isolated using ficoll gradient centrifugation and cultured for the indicated time periods. Apoptosis was determined using annexin V and propidium iodide (PI) labeling and flow cytometry. NF-B activation was examined using gel mobility shift assay and confocal microscopy. Expression levels of inhibitory apoptosis proteins (IAPs) including cIAP1, cIAP2, XIAP and Survivin, and Bcl-2 family members such as Bcl-xl and Bad, were determined by Western blotting and/or RT-PCR, real-time PCR. The results showed that in culture, the decrease in apoptosis of neutrophils from thermally injured rats was prevented in the presence of PI-3 kinase inhibitors, wortmannin and LY294002. There was up-regulation of PKB and Bad phosphorylation and NF-B activation in fMLP stimulated neutrophils from thermally injured rats compared to sham group. Increased Bad phosphorylation and NF-B activation were also attenuated by wortmannin. Bcl-xl expression in neutrophils was upregulated with thermal injury, and inhibited in the presence of wortmannin. However, the expression of IAP family members was neither affected by thermal injury, nor inhibited by wortmannin. These data suggest that the delay in neutrophil apoptosis with thermal injury is partly caused by activation of PI-3 kinase/PKB signaling and NF-B, which appeared to be related to the increased Bcl-xl expression and phosphorylation of Bad, but not IAPs expressions.