http://en.wikipedia.org/wiki/Tryptophan

http://www.drugs.com/mtm/l-tryptophan.html

http://www.drugs.com/cons/l-tryptophan.html

http://www.caoh.org/l-tryptophan.html

http://health.yahoo.com/nutrition-supplements/l-tryptophan/healthwise--d04732a1.html

http://www.cocoonnutrition.org/catalog/page_tryptophan.php

http://www.lef.org/fda/fdaban95.html

http://www.ceri.com/trypto.htm

http://www.iherb.com/ProductDetails.aspx?c=1&pid=7276&at=0

http://www.drhoffman.com/page.cfm/529