Photooxidation of multivitamin solutions results in the generation of peroxides. Because peroxides are associated with hepatic steatosis and fibrosis as well as cholestasis, we questioned whether multivitamins are implicated in hepatic complications of parenteral nutrition. Guinea pig pups were assigned to groups receiving intravenously either total parenteral nutrition, photo-protected or not, or a control solution (5% dextrose ϩ 0.45% NaCl) supplemented with either a) multivitamins; b) photo-protected multivitamins; c) multivitamins without riboflavin; or d) peroxides (H 2 O 2 , tert-butylhydroperoxide). After 4 d, liver was sampled for histology and isoprostane-F 2␣ levels, a marker of radical attack. Multivitamins as well as total parenteral nutrition were associated with steatosis (scored 0 -4), the severity of which was reduced (p Ͻ 0.05) by photo protection. Although H 2 O 2 is the major peroxide contaminating multivitamins, it did not induce steatosis scores different than the controls. Compared with controls, hepatic isoprostane-F 2␣ content increased in animals infused with H 2 O 2 (p Ͻ 0.05), but not in those infused with Multi-12 pediatric multivitamins or total parenteral nutrition. Results suggest that peroxides and/or free radicals are not mediators of the induction of steatosis observed with infusion of photo-exposed multivitamins, as there was no correspondence between histologic findings and hepatic levels of isoprostanes. It is suspected that a component of the multivitamin solution becomes hepato-toxic after photo-exposure, as indicated by the protective effect observed when withdrawing riboflavin. Photooxidation of multivitamins might be the common link between reports involving amino acids, lipids, and light exposure in the ethiology of hepatic complications of parenteral nutrition. Exposure of TPN solutions to light is linked to alterations in hepatobiliary function and histology in a perfused liver model (1) as well as in vivo (2). In the presence of light, the parenteral multivitamin preparation is the site of reactions between oxygen and electron donors, resulting in the generation of peroxides. Hydrogen peroxide (H 2 O 2 ), which is regarded as a key element in the oxygen toxicity of the cell, represents over 80% of peroxides generated in multivitamins (3). Organic peroxides have also been reported to contaminate solutions of parenteral nutrition (3-6). In parenterally fed neonates, the exposure of multivitamins to daylight is associated with an infused peroxide load and its urinary excretion (7). Peroxides have been linked to hepatic steatosis (8) and fibrosis (9), as well as cholestasis (10). Multivitamins and peroxides induce the same oxidant response in the lungs of guinea pig pups (11). The relative liver weight of these animals was 40% higher than controls (12), and histology revealed the presence of hepatic steatosis. We hypothesize that multivitamins might account for part of the role of light in TPN-related liver complications.Because of the catalytic role of photo-excited rib...