Because total parenteral nutrition with vitamins added to the glucose-amino acid mixture is often associated with a reduction in blood levels of vitamin A (retinol) during the routine treatment of many very low birth weight (VLBW) infants (less than 1500 gm), and because retinol losses in the plastic delivery system can be prevented by adding the vitamins to an intravenous lipid emulsion, seven VLBW infants with a mean birth weight of 900 gm (range 450 to 1360 gm) were given 40% of a unit dose vial, per kilogram of body weight, of a multivitamin preparation (M.V.I. Pediatric) (280 micrograms retinol; 160 IU vitamin D; 2.8 mg tocopherol; 0.68 mg riboflavin) in a lipid emulsion, Intralipid. After treatment with the intralipid-vitamin mixture for 19 to 28 days, plasma vitamin A (retinol) concentrations increased significantly from 11.0 +/- 0.76 (mean +/- SEM) before intralipid to 19.2 +/- 0.97 micrograms/dl after the intralipid-vitamin mixture (p less than 0.01); 25-hydroxyvitamin D concentrations increased from an initial value of 12.6 +/- 2.6 to 20.2 +/- 1.9 mg/dl (p less than 0.01); alpha-tocopherol concentrations increased from an initial value of 0.31 +/- 0.06 to 2.44 +/- 0.13 mg/dl (p less than 0.01); and riboflavin levels increased from 64.1 +/- 7.8 ng/ml to concentrations between 20 and 100 times the initial level. Erythrocyte riboflavin levels increased from 71.8 +/- 14 initially to 166 +/- 41 ng/gm hemoglobin, and erythrocyte flavin-adenine dinucleotide levels increased similarly from 972 +/- 112 initially to 2005 +/- 294 ng/gm hemoglobin. These results show that the addition of M.V.I. Pediatric to Intralipid decreases the extensive in vivo loss of retinol and is associated with an increase in plasma retinol concentrations in VLBW infants. The daily doses of vitamins D (160 IU/kg) and E (2.8 mg/kg) appear sufficient, but the dose of vitamin A (280 micrograms/kg) is insufficient to raise blood levels of all infants into the normal range. The current dose of riboflavin is excessive and may be harmful.