Initially considered the main endogenous anorexigenic factor, fat-derived leptin turned out to be a markedly pleiotropic hormone, influencing diverse physiological processes. Moreover, hyperleptinemia in obese individuals has been linked to the onset or progression of serious disorders, such as cancer, autoimmune diseases, and atherosclerosis, and antagonizing peripheral leptin's signalization has been shown to improve these conditions. To develop an antibody-based leptin antagonist we have devised a tailored panning procedure and screened two phage display libraries of single chain variable antibody fragments (scFvs) against recombinant leptin receptor. One of the scFvs was expressed in Escherichia coli and its interaction with Ieptin receptor was characterized in more detail. It was found to recognize a discontinuous epitope and to compete with leptin for receptor binding with IC50 and K-d values in the nanomolar range. The reported scFv represents a lead for development of leptin antagonists that may ultimately find use in therapy of various hyperleptinemia-related disorders. (C) 2014 Elsevier Inc. All rights reserved.