The theory that raised blood homocysteine is a major factor in the development of cardiovascular disease was initially rejected by the medical establishment. Trials of a treatment to lower homocysteine in moderately advanced disease have failed to show benefits (except in those not treated with anti-platelet drug), but there is mounting evidence for a role in treatment of very early disease and as a preventive strategy. Recent evidence has shown that lowering of high blood homocysteine significantly slows cognitive decline and the brain shrinkage associated with Alzheimer’s disease. This is a test that should be done more frequently by National Health Service (NHS) general practitioners and private practitioners.