The present study was designed to investigate whether the β-adrenergically mediated blood flow response of abdominal subcutaneous adipose tissue (per unit adipose tissue weight) was altered in obesity and to study the effect of weight reduction on this response. Body composition (underwater weighing) and fat blood flow were determined in a group of lean (n = 9; % body fat, 11.6 ± 3.9) and obese (n = 9; % body fat, 28.3 ± 1.8) subjects. In seven obese subjects, measurements were also performed after a 4-week period of weight reduction induced by a very-low-calorie diet (% body fat after diet 23.4 ± 3.3). After an overnight fast, abdominal subcutaneous fat blood flow was determined by the ¹³³xenon washout technique during a 30-minute period of supine rest and during 30-minute periods of infusion of the β-agonist isoprenaline (ISO) with and without simultaneous infusion of the β₁-blocker atenolol (AT). Basal abdominal fat blood flow was significantly higher in lean as compared with obese subjects, whereas weight reduction significantly increased basal fat blood flow (obese v reduced-obese, P < .05). There was a significant increase in abdominal fat blood flow as a result of ISO infusion in lean and obese subjects before and after weight reduction. During ISO + AT infusion, abdominal fat blood flow was still significantly increased as compared with control values in lean and obese subjects. The increase in blood flow during ISO was significantly higher in lean subjects than in obese subjects, whereas the ISO + AT-induced blood flow response was comparable. These data suggest that especially the β₁-mediated blood flow response is blunted in obese subjects. Although the increase in the ISO-induced blood flow response was not significantly different after as compared with before the diet, there was a significant positive relationship between the decrease in percent body fat and the change in the ISO-mediated abdominal blood flow as a result of weight loss (P < .05). In conclusion, the present study shows that the β-adrenergically mediated abdominal fat blood flow response (expressed per unit weight) is diminished in obesity. This decreased blood flow response tended to change in a direction toward the condition seen in lean subjects after partial weight reduction.