OBJECTIVE-An emerging model of metabolic syndrome and type 2 diabetes is of adipose dysfunction with leukocyte recruitment into adipose leading to chronic inflammation and insulin resistance (IR). This study sought to explore potential mechanisms of inflammatory-induced IR in humans with a focus on adipose tissue. RESEARCH DESIGN AND METHODS-We performed a 60-h endotoxemia protocol (3 ng/kg intravenous bolus) in healthy adults (n ϭ 20, 50% male, 80% Caucasian, aged 27.3 Ϯ 4.8 years). Before and after endotoxin, whole-blood sampling, subcutaneous adipose biopsies, and frequently sampled intravenous glucose tolerance (FSIGT) testing were performed. The primary outcome was the FSIGT insulin sensitivity index (S i ). Secondary measures included inflammatory and metabolic markers and whole-blood and adipose mRNA and protein expression. RESULTS-Endotoxemia induced systemic IR as demonstratedby a 35% decrease in S i (3.17 Ϯ 1.66 to 2.06 Ϯ 0.73 ϫ 10 Ϫ4 [U ⅐ ml Ϫ1 ⅐ min Ϫ1 ], P Ͻ 0.005), while there was no effect on pancreatic ␤-cell function. In adipose, endotoxemia suppressed insulin receptor substrate-1 and markedly induced suppressor of cytokine signaling proteins (1 and 3) coincident with local activation of innate (interleukin-6, tumor necrosis factor) and adaptive (monocyte chemoattractant protein-1 and CXCL10 chemokines) inflammation. These changes are known to attenuate insulin receptor signaling in model systems.CONCLUSIONS-We demonstrate, for the first time in humans, that acute inflammation induces systemic IR following modulation of specific adipose inflammatory and insulin signaling pathways. It also provides a rationale for focused mechanistic studies and a model for human proof-of-concept trials of novel therapeutics targeting adipose inflammation in IR and related consequences in humans.