Several growth factors are implicated in sleep regulation. Epidermal growth factor (EGF) is found in the brain, and it influences the production of several sleep-promoting substances. We determined, therefore, whether administration of exogenous EGF affected spontaneous sleep in rabbits. Twenty-five rabbits were implanted with electroencephalographic electrodes, a brain thermistor, and an intracerebroventricular guide cannula. Three doses of EGF (0.5, 5, and 25 µg) were used. The animals were injected intracerebroventricularly with saline as control and one dose of EGF on 2 separate days. Five and twenty-five micrograms of EGF enhanced non-rapid eye movement sleep and increased brain temperature. The 25-µg dose of EGF also inhibited rapid eye movement sleep across the 23-h postinjection recording period. Results are consistent with the hypothesis that EGF, like other growth factors, could be involved in sleep regulation.