Plasma B<sub>12</sub>, folate, B<sub>6</sub> and thiamine, and red blood cell folate, thiamine and niacin levels were monitored for a period of 6 months in 15 clinically stable, chronic hemodialysis patients who were not supplemented with the water-soluble vitamins. Microbiological assays were used to determine the blood levels of the water-soluble vitamins. Over the period of 6 months, none of the patients had plasma or red cell vitamin levels below the normal range. No appreciable changes were observed in the plasma and red blood cell vitamin levels before and after dialysis in 5 patients. This study showed that chronic hemodialysis patients are able to maintain normal plasma and red cell levels of some water-soluble vitamins without daily supplementation.