The molecular bases underlying burn- or critical illness-induced insulin resistance still remains unclarified. Muscle protein catabolism is a ubiquitous feature of critical illness. Akt/PKB plays a central role in the metabolic actions of insulin, and is a pivotal regulator of hypertrophy and atrophy of skeletal muscle. We, therefore, examined the effects of burn injury on insulin-stimulated Akt/PKB activation in skeletal muscle. Insulin-stimulated phosphorylation of Akt/PKB was significantly attenuated in burned compared to sham-burned rats. Insulin-stimulated Akt/PKB kinase activity, as judged by immune complex kinase assay and phosphorylation status of the endogenous substrate of Akt/PKB, glycogen synthase kinase-3 (GSK-3), was significantly impaired in burned rats. Furthermore, insulin consistently failed to increase the phosphorylation of p70S6 kinase, another downstream effector of Akt/PKB, in rats with burn injury, whereas phosphorylation of p70S6 kinase was increased by insulin in controls. The protein expression of Akt/PKB, GSK-3 and p70S6 kinase was unaltered by burn injury. However, insulin-stimulated activation of extra-cellular-regulated protein kinase (ERK), a signaling pathway parallel to Akt/PKB was not affected by burn injury. These results demonstrate that burn injury impairs insulin-stimulated Akt/PKB activation in skeletal muscle, and suggest that attenuated Akt/PKB activation may be involved in deranged metabolism and muscle wasting observed after burn injury.