Human leptin is a 16-kDa nonglycosylated hormone that is produced in mature adipocytes. Leptin acts primarily in the hypothalamus to reduce food intake and body weight. In ob/ob mice, the gene encoding leptin is mutated, resulting in morbid obesity and associated abnormalities, including hyperphagia, hypothermia, diabetes and infertility. The function of leptin in regulating appetite and metabolism, as well as the possibility of using leptin as a therapeutic agent, are currently under intense investigation.