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I nsulin resistance is a major factor in the pathogenesis of type 2 diabetes and may involve fat-induced activation of a serine kinase cascade involving IKK-β. To test this hypothesis, we first examined insulin action and signaling in awake rats during hyperinsulinemic-euglycemic clamps after a lipid infusion with or without pretreatment with salicylate, a known inhibitor of IKK-β. Whole-body glucose uptake and metabolism were estimated using [3-³H]glucose infusion, and glucose uptake in individual tissues was estimated using [1-¹⁴C]2-deoxyglucose injection during the clamp. Here we show that lipid infusion decreased insulin-stimulated glucose uptake and activation of IRS-1–associated PI 3-kinase in skeletal muscle but that salicylate pretreatment prevented these lipid-induced effects. To examine the mechanism of salicylate action, we studied the effects of lipid infusion on insulin action and signaling during the clamp in awake mice lacking IKK-β. Unlike the response in wild-type mice, IKK-β knockout mice did not exhibit altered skeletal muscle insulin signaling and action following lipid infusion. In summary, high-dose salicylate and inactivation of IKK-β prevent fat-induced insulin resistance in skeletal muscle by blocking fat-induced defects in insulin signaling and action and represent a potentially novel class of therapeutic agents for type 2 diabetes.