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. Originally discovered in the mouse, the cDNA for leptin has been so far cloned from a variety of species including human, rat, cow, chicken, pig, sheep and dog.