The experimental design is a prospective, two-arm, randomized, double blind study, stratified for medical center and whether the patient has chronic renal failure or end-stage renal disease. In each arm 1003 patients will ingest daily a capsule containing either 40mg of folic acid, 100mg of pyridoxine and 2mg of vitamin B12, or placebo. We will use stratified randomization to ensure that the treatment is balanced within the end-stage renal disease patients and chronic renal failure patients.