The primary objective of this study is to test the hypothesis that administration of folate, pyridoxine (vitamin B6) and cyanocobalamin (vitamin B12) in high doses to patients with advanced chronic renal failure or end stage renal disease and abnormally high plasma homocysteine levels will lower the homocysteine levels and the death rate compared to patients who receive placebo. The secondary objective is to test the hypothesis that intake of the vitamins compared to placebo decreases the incidence of myocardial infarction, disabling stroke, and amputation of a lower extremity and, in hemodialysis patients, thrombosis of the vascular access.