This 6 year study will require an accrual phase of 2 years and a treatment phase lasting a minimum of 4 years. Patients will be screened by their plasma homocysteine concentration. They must have a level of at least 15 uM/L to be enrolled in the study. The study nurse will evaluate each patient at 3 months. Thereafter, patients will be contacted by phone, or mail if they prefer, at 3-month intervals by coordinators at a central location. Secondary endpoint events, hospitalization, onset of dialysis, and death or other reason for exit from the study will be recorded on standard forms. Plasma homocysteine levels will be obtained at 3 months in all patients.