The author states that the use of the amino acid L-tryptophan as a hypnotic might avoid the problems of nonspecificity in the currently used CNS depressants because L-tryptophan is chosen on the basis of the chemistry of normal sleep rather than on a purely empirical basis. He reviews nine studies from his laboratory dealing with the effects of L-tryptophan on sleep. Studies in rats, normal human subjects, and subjects with mild insomnia all demonstrate that L-tryptophan reduces sleep latency. Polygraphic studies demonstrate that L-tryptophan, unlike hypnotics, does not produce distortions of sleep physiology when first administered, on long-term administration, or after withdrawal.