The study is to be conducted in patients with chronic renal failure and end-stage renal disease whose plasma homocysteine levels and incidence of cardiovascular death and disease are among the highest of all patient populations. By screening for patients with high plasma homocysteine concentrations and measuring the levels after 3 months, we will be able to determine if the hypothetical reduction in death and cardiovascular event rate is associated with a decrease in plasma homocysteine concentration.