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 + 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(2alpha) 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 < 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(2alpha) content increased in animals infused with H(2)O(2) (p < 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. Photo-oxidation 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.