* Dietary Supplement * Promotes Tissue Repair and Production of Antibodies, Hormones and Enzymes * 21st Century...for a Healthier Future 21st Century"s L-Lysine is an amino acid, which are the basic components of proteins synthesized in the body. They are essential in human nutrition. L-Lysine functions as an essential building block of all proteins and promotes tissue repair and production of antibodies, hormones, and enzymes.