Analysis of a structural model of the Leptin-LEPR complex using as a basis the complex formed by granulocyte-colony stimulator factor (GCSF) and its receptor G-CSF R (Hiroike et al., 2000) suggested that helices I and III of the human leptin structure were likely sites of interaction with the cytokine binding domain of leptin receptor (Gonzalez and Leavis, 2003). It is believed that the Leptin receptor (LEPR) is a dimer constitutively bound in a complex with JAK2 kinase (Couturier and Jockers 2003). It has been proposed that one molecule of Leptin binds each monomer of LEPR (Luoh et al. 1997, Mistrik et al. 2004), however these suggestions need further proof becasue the structure of the Leptin:LEPR complex has not yet been solved.