Background: Leptin has been shown to be an integral component of energy homeostasis and regulation of body weight. Leptin regulates adipose tissue mass and correlates with the fat mass, however the circulating levels are altered by energy intake. Research on the physiological function of leptin has primarily focused on its role in the pathogenesis of obesity. However, its role in the negative energy imbalance is unclear. Increased energy expenditure is a primary factor in the reduced growth in infants with cyanotic congenital heart disease. The objective of this study was to examine the possible role of leptin on growth and nutrition in children with cyanotic and acyanotic congenital heart disease. Methods and Results: In this study, plasma leptin levels, nutritional and growth status were evaluated in 28 cyanotic and 20 acyanotic patients with congenital heart disease. Although standard deviation (S.D.) of height (P<0.01), mid arm circumference (MAC) (P<0.001) and body mass index (BMI) (P<0.05) were significantly low in cyanotic group, plasma leptin levels were similar. Energy intake was high in cyanotic group. In both cyanotic and acyanotic group, plasma leptin levels were correlated with BMI (r: 0.388, P<0.05 and r: 0.789, P<0.001, respectively). In addition, leptin levels were significantly correlated with the height (r: 0.415, P<0.05), MAC (r: 0.482 P<0.05) and BMI (r: 0.377, P<0.05) S.D. in cyanotic subjects. Conclusions: Our results suggest that the leptin regulating axis is intact in cyanotic patients and leptin does not contribute to the cachexia of cyanotic heart disease. (C) 2003 Elsevier Ireland Ltd. All rights reserved.