The chemical formation, toxicity, and pharmacokinetics of 5-hydroxymethylfurfural (HMF) and certain other decomposition products found in parenteral solutions are reviewed. Heat sterilization-induced hexose decomposition to furan derivatives is promoted at low pH. Based upon infusion studies with rats and dogs, HMF does not appear to be acutely toxic at concentrations ordinarily encountered in parenteral infusion solutions (e.g., 10 mg/liter). Dosages of parenterally administered HMF exceeding 75 mg/kg body wt have led to some toxic effects, including increased activity of hepatic enzymes, altered serum-protein fractions, increased relative spleen weight, and hepatic fatty degeneration. Approximately 50% of parenterally administered HMF is oxidized and eliminated by the kidneys. From a clinical standpoint, the amount of HMF formed as a result of the heat sterilization of parenteral solutions containing hexoses does not seem to pose any significant toxicologic problem.