This study represents an initial attempt to define intravenous vitamin requirements in adult patients receiving total parenteral nutrition (TPN). We have investigated two different vitamin formulations for their ability to maintain normal circulating blood levels of vitamins A, C, E, B12, folic acid and riboflavin. Administration of 1.1 ml of Multi-Vitamin Infusion (MVI) solution supplemented with 100 microgram of folic acid, 10 microgram of vitamin b12, and 100 mg of vitamin C, per liter of TPN infusate (patients received an average of about 3 liters/day), maintained normal or higher than normal levels of vitamins C, B12, and riboflavin, but resulted in less-than-normal levels of vitamins A, E, and folic acid. Increasing the amount of MVI to 1.4 ml and the folic acid to 200 microgram, and decreasing the ascorbic acid to 70 mg and vitamin B12 to 5 microgram/liter of TPN infusate, resulted in normal blood levels of all tested vitamins within two weeks after initiating TPN therapy, and normal blood levels were then maintained at this dosage for additional periods of time up to three weeks.