Vitamins are essential in total parenteral nutrition (TPN), their importance being highlighted by repeated past documentation of various vitamin deficiencies particularly in patients on long-term parenteral nutrition therapy. This study evaluated the efficacy of water- (Soluvit) and fat-soluble (Vitalipid) vitamin supplementation in patients receiving total parenteral nutrition using the three in one 3-liter bag system. All patients received water-soluble vitamin supplements daily. Fat-soluble vitamin supplements were administered on a daily or twice weekly basis. Twenty-two patients were studied. In seven of the 22 patients vitamin status was assessed on more than one occasion during TPN support, thus bringing the total number of observations to 30. The mean duration of TPN support was 35 days. Eight of the observations were made during less than 10 days, three between 11-19 days, 15 between 20-60 days, and four during more than 60 days of TPN support. Biochemical deficiency as judged by subnormal enzyme activity or vitamin levels were present in 10% of the patients for thiamin, 3% for riboflavin, and 6% for nicotinic acid. By contrast 83% of the patients had low plasma vitamin C and B6 levels. Low plasma vitamin A and E levels were also present in 43 and 40% of the patients, respectively. According to the plasma concentrations of the vitamins studied it would appear that the commercial vitamin preparations used in this study are inadequate in maintaining optimal vitamin status.(ABSTRACT TRUNCATED AT 250 WORDS)