The leptin-deficient (ob/ob) or (Lepob/Lepob) mouse model develops hyperphagia, obesity, transient hyperglycaemia, high serum insulin, elevated numbers of pancreatic beta cells, lowered LH [6], GH [4] in the serum but higher hypophyseal Prl protein content [10]. The gene discussed is LEP; the disease is obesity due to melanocortin 4 receptor deficiency.