Leptin is thought to modulate feeding behaviour, body weight and energy metabolism by acting through specific cellular receptors. Derangements of leptin production have been repeatedly reported in patients with anorexia nervosa (AN) or bulimia nervosa (BN), but no information has been provided on the functional status of leptin receptors in these disorders. Therefore, we measured plasma levels of leptin and its soluble receptor (Ob-Re) in a total of 130 women, including 22 patients with AN, 45 patients with BN, 18 patients with the binge-eating disorder (BED), 12 non-binge eating obese women and 33 healthy women. Circulating leptin was drastically reduced in underweight anorexics and normal-weight bulimics, but increased in overweight BED patients and non-binge-eating obese women. Conversely, plasma levels of Ob-Re were significantly increased in patients with AN or BN, but decreased in BED and non-binge-eating obese women. Significant inverse correlations were detected between plasma levels of leptin and those of Ob-Re in all the subject groups, except in non-binge-eating obese subjects. These results show, for the first time, that opposite modifications occur in circulating levels of leptin and Ob-Re across the eating-disorder spectrum. The relevance of these findings to the pathophysiology and treatment of eating disorders remains to be elucidated.