Leptin is an adipose tissue hormone which is a signal for the regulation of food intake and thus of body weight. Precise mechanisms which regulate leptin levels are not known so far. The objective of the presented work was to investigate leptin levels in children with two controversial nutritional disorders - anorexia nervosa and obesity, in relation to their body mass index. In girls with anorexia nervosa (n = 26, age 15.18 ± 0.45 years, weight deficit 23.96 ± 1.59%), obesity (n = 26, age 14.53 ± 0.63 years, overweight 54.94 ± 3.29% as compared with normal for the given age group) blood specimens were take to examine basal leptin levels. The control group was formed by 15 healthy girls (n = 15, age 14.41 ± 0.52 years, body weight 2.77 ± 2.03%). The leptin levels were assessed by the RIA method and compared mutually. The mean leptin values in patients with anorexia nervosa were significantly lower (1.91 ± 0.23 ng/ml) as compared with healthy children (6.07 ± 0.91 ng/ml, p < 0.001). The leptin levels in obese children (23.61 ± 2.40 ng/ml) were significantly higher. The authors revealed also a significant positive correlation between the leptin level and body mass index incl. the percentage deviation from ideal body weight (r = 0.86) and the multiple of the standard deviation of BMI for the pertinent age group of girls (r = 0.84). On analysis of different groups the correlation was less close - in the group of obese girls the authors found a significant positive correlation between the leptin value and the percentage deviation from ideal body weight (r = 0.60). The leptin level of girls with anorexia nervosa did not correlate with body weight regardless whether expressed as the absolute value (r = 0.08), as the percentage deviation from ideal body weight (r = 0.14) or as BMI SD (r = 0.25). Leptin plays an important role in the regulation of body weight of patients with chronic nutritional disorders and its levels draw attention to the nutritional status and adipose tissue status. It must be stated that leptin is an important but by far not the only factor which participates in the etiopathogenesis of these two multifactorial nutritional disorders. Therefore leptin cannot be considered a suitable parameter for investigation of the clinical condition of patients during the period of chronic extreme starvation, as at that time its levels can be modulated by other factors.

        Key words: leptin, anorexia nervosa, obesity, body mass indexes