Besides commonly used rodents, there are a variety of experimental animals involved in the study of sleep, including cat, drosophila, monkey, zebrafish and so on. Rodents are used widely in sleep studies, because it is easy to make sleep models on rodents by physical and chemical methods. Among them, transgenic mice are mainly used for drug development and of sleep mechanism study. Drosophila and zebrafish are usually applied to genetic studies of sleep. Using cats for sleep study has a long history, and they are now often used to quantify in vivo endogenous neurotransmitters. Monkeys have a similar sleep structure to humans, so that they are widely used to study the relationship between sleep and neurobiology, behavioral pharmacology and so on. Animals are selected for experiments on the basis of research purpose, because each kind of animals has its own unique physiological characteristics.