Previous results have demonstrated sleep-inducing effects of L-tryptophan in doses of 1 to 15 g at bedtime. The present laboratory study extends the dose-response curve downward, comparing doses of 1/4 g, 1/2 g, and 1 g of L-tryptophan with placebo, in 15 mild insomniacs (subjects who reported sleep latencies of over 30 minutes). One gram of L-tryptophan significantly reduced sleep latency: the lower doses produced a trend in the same direction. Stage IV sleep was significantly increased by 1/4 g of L-tryptophan. These results at low doses have interesting implications since the normal dietary intake of L-tryptophan is 1/2 g to 2 g per day.