AIMS/HYPOTHESIS: The aim of this study was to investigate whether the beta2-adrenergically mediated increase in interstitial glycerol concentrations (used as an indicator of local lipolysis) was impaired in the skeletal muscle (the gastrocnemius muscle) of obese subjects compared with in that of lean subjects, and whether any differences in muscle lipolysis were related to differences in intramyocellular muscle triglyceride content. METHODS: A microdialysis experiment was performed in the gastrocnemius muscle of eight lean and eight obese men (body fat 22.1+/-1.6% vs 32.7+/-1.6% respectively). After determining baseline extracellular glycerol concentrations, the probe was perfused with increasing concentrations of the beta2-agonist, salbutamol (doses of 1, 10 and 100 micromol/l for 45-min periods). Local blood flow was determined using the ethanol dilution technique. Intramyocellular lipid content was determined using 1H-magnetic resonance spectroscopy. RESULTS: Compared with that in lean subjects, the beta2-adrenergically mediated increase in glycerol concentrations (absolute and percentage change) was blunted in obese subjects (at 100 micromol/l of salbutamol, percentage change 12.0+/-12% vs 48+/-12%, p<0.05). The decrease in ethanol out:in ratio was less pronounced in the obese individuals ( p<0.05), indicating a diminished increase in local muscle blood flow. Intramyocellular lipid content was comparable in both groups. CONCLUSIONS/INTERPRETATION: The capacity to increase skeletal interstitial glycerol concentrations during direct beta2-adrenergic stimulation is impaired in obese subjects with normal intramyocellular concentrations, suggesting that this may be an early event in the process of triglyceride accumulation.