Homocysteine (Hey) and folate levels before and after hemodialysis (HD) were measured in blood from 31 patients with chronic renal failure (CRF). A multivitamin with folic acid (FA) was prescribed to 20 patients. Hey and folate were measured by HPLC-fluorometric and microbiological methods, respectively. Mean plasma Hey declined from 36.8 to 24.2 nmol/L during a 4-hr HD, indicating that Hey can be partly removed by HD. Mean plasma folate level before HD was 46.4 nmol/L and decreased to 25.9 nmol/L after HD, while mean red blood cell (RBC) folate did not change (1,295 and 1,385 nmol/L before and after HD, respectively). There were significantly negative correlations between Hey and RBC folate before (r = -0.46, p < 0.01) and after HD (r = -0.41, p < 0.03), while plasma folate showed a significant correlation with Hey levels only after HD (r = -0.43, p < 0.02). All patients had Hey levels over 12.0 μmol/L before HD, and only three of 31 had their Hey lower than 12.0 /unol/L after HD. Although significant correlations existed between Hey and folate, CRF patients appeared to have adequate folate nutriture judged by blood folate levels. It remains to be determined whether additional FA administration would reduce Hey or is there an altered Hey metabolism in CRF patients. Since there is a high incidence of cardiovascular disease among CRF patients, it is necessary to investigate the mechanism(s) of altered Hey metabolism in CRF patients.