['The authors found considerably lower plasma total homocysteine (tHcy) concentrations in patients with end-stage renal disease (ESRD) on maintenance hemodialysis, who routinely received high-dose parenteral vitamin B12, than in comparable patients receiving much higher doses of folic acid but only replacement-dose oral vitamin B12. They therefore sought prospective evidence that high-dose parenterally administered vitamin B12 may partially ameliorate renal failure-associated hyperhomocysteinemia.', 'Open phase 2 clinical trial.', 'Outpatient hemodialysis unit.', 'Fourteen clinically stable patients on maintenance hemodialysis with normal baseline serum vitamin B12 concentrations.', 'Three parenteral injections of 1 mg vitamin B12 given at 4-week intervals.', 'Plasma tHcy and serum vitamin B12 concentrations were measured before, during and 7 months after the termination of vitamin B12 therapy.', 'The mean (and standard error) baseline plasma tHcy was 26.5 (1.8) micromol/L. The plasma tHcy value fell successively after each vitamin injection to reach a value of 23.6 (1.6) micromol/L 1 month after the final injection (p < 0.05), while the serum vitamin B12 concentration increased from 471 (42) pmol/L to 890 (74) pmol/L (p < 0.05). Seven months after the final injection, the serum B12 concentration had fallen and tHcy had risen to near their original values.'] Does parenteral vitamin B12 reduce hyperhomocysteinemia in end-stage renal disease?