Rat models are an alternative to mice that may enable the creation of new gene disruptions that are unavailable in the mouse. These models will complement existing transgenic mouse models. Comparing mouse and rat models can allow the distinction between rodent-specific and general mammalian phenotypes. Although mice have been the animal model of choice for most geneticists, the rat has traditionally been favored by physiologists and pathologists. In many applications the rat is a better animal model for human disease. Their larger size make rats more conducive to study by instrumentation, and facilitates manipulation such as blood sampling, studying nerve conduction or performing surgery. In addition, rats have a physiology more similar to humans than mice do. For example, rats have a heart rate similar to that of humans, while mice have a heart rate five to ten times as fast. Rats have been used as important models for human cardiovascular disease, diabetes, arthritis, and many autoimmune and behavioral disorders. Rat models are superior to mouse models for testing the pharmacodynamics and toxicity of potential therapeutic compounds, partially because the number and type of many of their detoxifying enzymes is very similar to those in humans. For all of these reasons, the rat is an important model for human disease and can be used by academic researchers and pharmaceutical companies for functional genomics and drug discovery.