The article discusses the importance of sleep in animals and the lack of understanding about its homeostatic regulation. Drosophila has been used as a model for genetic studies of sleep, and recent research has identified genes and brain regions involved in sleep regulation. However, the role of D-Ser, a neurotransmitter, in sleep regulation is unclear. Through a genetic screen and thorough investigation, the study found that D-Ser regulates sleep through NMDAR1 and that the intestine plays a novel role in sleep regulation. The synthases, oxidases, and receptor of D-Ser are expressed in both the central nervous system and the intestine, but intestinal expression is important for sleep regulation. These findings suggest that D-Ser produced by intestinal SR promotes sleep through NMDAR1 in Drosophila.