Recent advances in transgenic technology have yielded various animal models for human diseases. With the establishment of embryonic stem cell technology as well as previous microinjection techniques, subtle and precise alterations can now be achieved using mice and other animals. However, there are still few models that provide insight into human obesity and body weight regulation. We will briefly review the regulation of appetite and body weight and the applications of transgenic technology to human obesity disorders, with particular emphasis on peptide hormones and neurotransmitters.