Background: Leptin is a protein mainly secreted by adipocytes, and the major function of leptin was its role in body weight regulation. In humans, there was a strong correlation between leptin and nutritional parameters, such as body mass index (BMI) and fat mass (FM). Administration of recombinant leptin to ob/ob mice, which have a genetic defect in leptin production, reduces food intake, increases energy expenditure, and decreases body weight. It is suggested that increased levels of circulating leptin levels may contribute to anorexia and weight loss in pathologic conditions including chronic obstructive pulmonary disease (COPD). Recent studies have provided evidence for a link between leptin and proinflammatory cytokines such as TNF-α. Objective: This study aimed to detect serum leptin and TNF-α levels in COPD patients without weight loss during stable disease and acute exacerbation, and to investigate relationships between leptin, TNF-α and nutritional parameters at different stages of the disease. Material and Methods: 26 stable COPD patients, 16 COPD patients with acute exacerbation and 15 control subjects participated in this study. To eliminate the effects of sex differences, all patients and controls were male. BMI, percent ideal body weight, percent FM, sum of skinfold tickness and serum leptin and TNF-α levels were measured in all participants. Leptin and TNF-α levels were measured by ELISA. Results: Serum leptin and TNF-α levels were significantly higher in the patients experiencing exacerbation than in the stable patients and controls. Although leptin levels were lower and TNF-α levels were higher in the stable patient group than in the controls, these differences were not statistically different. Leptin levels were significantly correlated with the nutritional parameters in both control and stable groups. However, in patients with acute exacerbation, a correlation between leptin and nutritional parameters was not found. There was no significant relationship between TNF-α and nutritional parameters in the three groups. In addition, while there was no correlation between leptin and TNF-α levels in the stable and control groups, a significant positive correlation was observed in patients with exacerbation. Conclusion: In conclusion (1) elevated TNF-α levels may be related to increased inflammation in patients, (2) circulating TNF-α levels were associated with increased leptin levels and (3) although leptin and nutritional parameters were correlated in the stable COPD patients, the correlation was weaker compared to controls, and during an exacerbation it disappeared completely. Therefore, inappropriately increased levels of leptin and TNF-α noted during recurrent acute exacerbations in patients with COPD may lead to changes in nutritional parameters and body weight in the course of the disease. Copyright © 2004 S. Karger AG, Basel.