Sepsis is associated with muscle wasting, mainly reflecting increased muscle proteolysis. Recent studies suggest that inhibition of GSK-3β activity may counteract catabolic stimuli in skeletal muscle. We tested the hypothesis that treatment of muscles from septic rats with the GSK-3β inhibitors LiCl and TDZD-8 would reduce sepsis-induced muscle proteolysis. Because muscle wasting during sepsis is, at least in part, mediated by glucocorticoids, we also tested the effects of GSK-3β inhibitors on protein degradation in dexamethasone-treated cultured myotubes. Treatment of incubated extensor digitorum longus muscles with LiCl or TDZD-8 reduced basal and sepsis-induced protein breakdown rates. When cultured myotubes were treated with LiCl or one of the GSK-3β inhibitors SB216763 or SB415286, protein degradation was reduced. Treatment of incubated muscles or cultured myotubes with LiCl, but not the other GSK-3β inhibitors, resulted in increased phosphorylation of GSK-3β at Ser9, consistent with inactivation of the kinase and suggesting that the other inhibitors used in the present experiments inhibit GSK-3β by phosphorylation-independent mechanisms. The present results suggest that GSK-3β inhibitors may be used to prevent or treat sepsis-induced, glucocorticoid-regulated muscle proteolysis.