Angiotensin II (Ang II) applied to the interstitial space influences carbohydrate and lipid metabolism in a tissue specific fashion. Thus, endogenous Ang II may have a tonic effect on tissue metabolism that could be reversed with AT1 receptor blockade, particularly during adrenergic stimulation. We studied 14 obese men. They were treated for 10 days with the AT1 receptor blocker irbesartan or with placebo in a double-blind and cross-over fashion. At the end of each treatment period, we assessed skeletal muscle and adipose tissue metabolism using the microdialysis technique. The ethanol dilution technique was applied to follow changes in tissue blood flow. Measurements were obtained at baseline and during application of incremental isoproterenol concentrations through the microdialysis catheter. Blood pressure decreased from 133 ± 3 / 84 ± 3 to 128 ± 3 / 79 ± 2 mmHg (p=0.02 and 0.006 for systolic and diastolic blood pressure, respectively) with AT1 receptor blockade. Isoproterenol perfusion caused a dose-dependent increase in dialysate glycerol in adipose tissue and in skeletal muscle. Irbesartan slightly reduced the isoproterenol induced glycerol response in adipose tissue (p<0.05 by ANOVA). Ethanol ratio, interstitial glucose supply, and lactate production in adipose tissue and in skeletal muscle were similar with placebo and with irbesartan. We conclude that AT1 receptor blockade in obese men does not reveal a major tonic Ang II effect on interstitial glucose supply, lipolysis, or glycolysis in skeletal muscle, either at rest or during beta-adrenergic stimulation. Endogeneous Ang II may slightly increase adipose tissue lipolysis. The mechanism may promote the redistribution of triglycerides from adipose tissue towards other organs.