L-Lysine is classified as an essential amino acid; meaning the human body cannot synthesize lysine on its own and thus must rely on adequate dietary intake to function properly. Animal proteins, such as meats, poultry, and milk are rich sources of lysine; proteins from grains, such as wheat and corn, generally tend to be low in lysine. An exception is wheat germ, which contains high amounts of lysine. Lysine made its initial appearance on the U.S. dietary supplement market in the mid-1950s. Historically, there was interest in fortifying bread and other grain-based foods with lysine to improve the protein value for populations with lysine-poor diets. However, this broad-scale application did not materialize in the United States, not for any safety concerns regarding lysine fortification, but because the U.S. Food and Drug Administration (FDA) would not change the Standards of Identity for white bread.1 On the other hand, fortification of animal feeds with lysine has been a common practice since 1970, with current usage estimated at 800,000 tons/year globally.1-3 Today, lysine is a common human dietary supplement as well, typically in the form of lysine hydrochloride. Of the many biological functions requiring lysine, some notable applications include synthesis of connective tissues such as bone, skin, collagen, and elastin; synthesis of carnitine and resultant conversion of fatty acids to energy; support for healthy growth and development in children; and maintenance of healthy immune function, particularly with regard to antiviral activity. Concerning the latter, lysine is well known for its potential benefit in the management of Herpes simplex virus (HSV) infections. An interesting note concerning lysine is that it is involved in the browning or caramelization reaction applied to foods such as pastries, cereals, and desserts. When heated, lysine links with a reducing sugar (such as fructose, glucose, or lactose), creating a caramelized substance that, although desirable from a culinary perspective, renders lysine nearly impossible for the body to absorb. Consequently, caramelized foods are low in usable lysine.