Differences in fat cell size and function among adipose tissue depots are well known and may be important in the pathophysiology of the metabolic and cardiovascular complications of obesity. Since the newly discovered adipocyte hormone leptin is thought to be a central factor in the regulation of energy homeostasis, it may be interesting to know if there are regional differences in leptin production. The aim of this study was to compare the level of leptin expression in the omental and subcutaneous abdominal adipose tissue from obese humans. Adipose tissue samples were collected from 25 severely obese adults (mean BMI: 48.9 +/- 9.7 kg/m2) undergoing vertical gastric banding. Semi-quantitative determination of leptin mRNA by the RT-PCR technique showed significantly lower leptin expression in omental compared to subcutaneous abdominal adipose tissue (leptin/Sp1 ratio in omental vs. subcutaneous fat: 1.53 +/- 0.89 vs. 3.02 +/- 1.58, p < 0.01). Identical results were obtained when Northern blotting was applied in a subgroup. Leptin expression increased with age in omental adipose tissue (r = 0.42, p < 0.05), but not in subcutaneous tissue. No correlation was found between BMI or waist/hip ratio (WHR) and leptin expression in omental or subcutaneous adipose tissue. The regional difference in leptin expression was similar in the patients with impaired glucose tolerance/type-2 diabetes and those with normal glucose tolerance. In conclusion, the results of this study indicate that leptin expression is lower in omental than subcutaneous adipose tissue, possibly due to differences in fat cell size and/or sympathetic innervation.