5-hydroxymethylfurfural (HMF) is formed in the Maillard reaction when reduced sugars are heated in the presence of amino acids or proteins. It can also be formed during direct thermal dehydration of fructose and sucrose, without amino acids.HMF is found in high levels in coffee, bread, cereals, plums, caramel and formula. The daily intake of the compound is estimated to be between 30-150 mg pr person.Several in vitro experiments have demonstrated a week genotoxic effect of HMF. Other studies have identified increased aberrant crypt foci and micro adenomas in the colon of mice due to HMF treatment. To our knowledge there have not been published any previous reports on the genotoxicity of HMF in vivo until now.LacZ/wt and LacZ/Min mice treated with 750 mg/kg bw HMF by gavage or 500 mg/kg bw HMF by subcutaneous injection was sacrificed and their organs isolated to establish the genotoxic effect of HMF by measuring the mutant frequency and the ratio of size changes and amount of oxidative damage in the LacZ plasmid. This experiment also evaluated whether having a mutated Apc gene made the DNA more prone to damages after HMF treatment.HMF did not seem to affect the mutant frequency or lead to increased oxidative damage in the DNA. There is on the other hand a a significant difference in the ratio of size changes between HMF treated mice and control mice. Having a mutated Apc gene did not lead to increased sensitivity towards DNA damage. Over all, HMF is concluded not to be genotoxic in LacZ plasmid mice in this study. The low activity of sulfotransferases (SULT) in mice can be the reason for the negative results. It is recommended for a new research experiment to be carried out using transfected mice carrying human sulfotransferases (SULT mice).