All aspects of sleep sciences are included in this excellent resource text, with special reference to sleep substances and sleep modulators. The historical development of the theories of sleep are reviewed in conjunction with the technical problems. All candidate substances are overviewed as to their sites of presence, chemical nature, bioassay techniques, physiological and pharmacological effects. On the basis of a standardized methodology developed by the author, sleep-modulatory characteristics of some substances are compared and evaluated in quantitative terms. The sleep regulatory mechanisms, which are composed of complex neurohumoral subsystems, are analyzed from the results of recent neurophysiological and neuroendocrinological experiments. Furthermore, an evolutionary aspect of sleep substances is taken into consideration.