Leptin is a protein hormone produced by adipocytes. Its serum concentrations in the most of cases positively correlate with total body fat content. Serum leptin levels are increased in obese in comparison with lean subjects. Leptin levels in females are two or three times higher than in body mass index and age-matched males. The aim of our study was to investigate the serum leptin concentrations in females with protein-caloric malnutrition of various aetiology, the relationship between leptin levels and biochemical nutritional parameters and to compare the values with those of age-matched control group. Totally 12 patients with malnutrition of various aetiology and 14 control age-matched healthy subjects were included into the study. It was found that serum leptin levels were significantly decreased in malnutrition group in comparison with control group (3.09 +/- 1.33 ng.ml-1 vs 9.42 +/- 2.76 ng.,l-1, p < 0.05). A significant decrease in body mass index, serum total protein, albumin, prealbumin, cholesterol and triglycerides concentration was also found in malnutrition in comparison with control group. While a strong positive correlation between leptin concentrations and body mass index was found in control group (r = 0.72, p < 0.05), no statistically significant relation between leptin and body mass index was observed in malnutrition group. Furthermore, no significant relationship was found between serum leptin levels and serum total protein, albumin, prealbumin, cholesterol and triglycerides neither in control or in malnutrition group. We conclude that serum leptin levels in patients with malnutrition are significantly decreased in comparison with age-matched healthy control subjects. The loss of positive correlation between leptin and body mass index in malnutrition group is explainable by the changes of body composition in patient with malnutrition. The body mass index value in these patients reflects the total body fat content less precisely than in healthy controls.