This paper traces the history of the EEC Scientific Committee for Food's examination of available toxicological data on tert-butylhydroquinone (TBHQ). Studies of mutagenicity, metabolism, enzyme activities, reproduction and long-term toxicity and carcinogenicity are reviewed. The author concludes that dose level is an important factor in the induction of forestomach tumours. Further long-term toxicity testing of TBHQ is needed to evaluate its genotoxicity. However, since information is not available, an attempt is made to calculate the 'safety' margin between actual intake by man and the conventional no-effect level in dogs and rats.