The relationship of leptin to diminished appetite and weight loss has been investigated in many diseases. Diminished appetite and weight loss are the most apparent characteristics of patients with active lung tuberculosis and in this study the relation of leptin to such diminished appetite and weight loss has been investigated in patients with active lung tuberculosis before and after treatment. Twenty-five patients (7 female, 18 male) with active tuberculosis having an age range of 18-70 years (mean 47.48 +/- 15.36 y) and 25 normal individuals (9 female, 16 male) having an age range of 25-71 years (mean 44.60 +/- 13.80 y) were included in this study. Leptin levels, body mass index (BMI), body fat ratio (BFR), and waist hip ratio (WHR) were measured before and after 6 months of antituberculosis treatment. The same measurements were also made in the control group and the results were compared. While the pretreatment BMI (22.02 +/- 4.31 kg/m(2)) and BFR (16.60% +/- 9.30%) values in the patient group were significantly lower than in the control group, we found no difference in their pretreatment WHR values. Pretreatment leptin levels (3.49 +/- 3.34 mug/L) were significantly higher in patients with tuberculosis than in the control group (2.33 +/- 1.10 mug/L). Leptin levels were found to be significantly increased at the 6th month of antituberculosis treatment (5.65 +/- 5.41 mug/L) than the pretreatment values (p < 0.05). We observed an evident increase in BMI (24.10 +/- 4.87 kg/m(2)) and BFR (17.51% +/- 9.25%) due to antituberculosis treatment (p<0.05). This study suggests that leptin has a role in the diminished appetite and weight loss symptoms in patients with active lung tuberculosis.