Plasma levels of vitamins were determined in eight patients who were nourished with long-term enteral feeding using commercial formulas. The type and quantity of the formula were individually tailored to the patients' needs. Caloric intake (mean +/- SEM) amounted to 1564 +/- 97 kcal/day. Vitamins intake from the formulas, expressed as percent of Recommended Daily Allowances (RDA), was as follows: pantothenic acid, 222 +/- 44%; vitamin B12, 206 +/- 34%; vitamin C, 376 +/- 51%; thiamine, 207 +/- 34%; niacin, 207 +/- 34%; riboflavin, 207 +/- 34%; pyridoxine, 222 +/- 17%; biotin, 113 +/- 13%; vitamin A, 93 +/- 4%; and folic acid, 104 +/- 14%. Plasma levels of thiamine, riboflavin, pyridoxine, pantothenic acid, folic acid, and vitamin B12 were within normal limits in all patients. Two patients had lower than normal plasma levels of nicotinic acid despite the high intake. Plasma biotin levels were above normal in all patients, with a mean of 931 +/- 140 pg/ml (N: 200-500 pg/ml). Ascorbic acid levels were within or above normal, but no correlation with intake was found. Carotene levels were measured in five patients and found to be below the lower limit of normal, a reflection of lack of intake from the enteral formulas. The plasma vitamin A levels were normal in all patients. It is concluded that feeding with commercial enteral formulas results in normal plasma levels of vitamins in patients maintained on these formulas for over 6 months. The excessive amounts of vitamins in the formulas do not result in elevated plasma levels, except for Biotin.