Individuals with elevated homocysteine levels are at increased risk for cardiovascular disease and stroke, and neurodegenerative disorders such as Alzheimer's and Parkinson's diseases Homocysteine is a modified form of the amino acid methionine that is tightly regulated by enzymes requiring folate. By impairing DNA repair mechanisms and inducing oxidative stress, homocysteine can cause the dysfunction or death of cells in the cardiovascular and nervous systems. Dietary folate stimulates homocysteine removal and may thereby protect cells against disease processes. The enzymes involved in homocysteine and folate metabolism provide novel targets for drug discovery.