Vitamin A is the parent compound of retinoids, which regulate gene transcription by binding to nuclear retinoid receptors. Recently, it has been suggested that retinoid signaling pathways are important for adult neural function in health and disease. In this mini review we will summarize the molecular pathway of retinoid and experimental data on this pathway relating to sleep regulation, which suggests that retinoid signaling mechanism may be involved in the homeostatic component of sleep electroencephalogram. J. Med. Invest. 55: 1-8, February, 2008