The inhibitor of NF-kappaB (IkappaB) kinases (IKK1[alpha] and IKK2[beta]), the catalytic subunits of the IKK complex, phosphorylate IkappaB proteins on serine residues, targeting them for degradation and thus activating the transcription factor NF-kappaB. More recently, IKK2 has been implicated in mediation of insulin resistance caused by obesity, lipid infusion, and TNF-alpha stimulation, since salicylate and aspirin, known inhibitors of IKK activity, can reverse insulin resistance in obese mouse models. To further genetically elucidate the role of IKK2 in obesity-mediated insulin resistance, we have conditionally inactivated the mouse IKK2 gene in adult myocytes by Cre-loxP-mediated recombination in vivo. We have investigated the development of obesity-induced insulin resistance in muscle-specific IKK2 knockout mice and mice exhibiting a 50% reduction of IKK2 expression in every tissue and have found that, after gold thioglucose treatment, wild-type and mutant mice developed obesity to a similar extent. Surprisingly, no difference in obesity-induced insulin resistance was detectable, either at a physiological or at a molecular level. Moreover, impaired glucose tolerance resulting from a high-fat diet occurred to the same degree in control and IKK2 mutant mice. These data argue against a substantial role for muscular IKK2 in mediating obesity-induced insulin resistance in these models in vivo.