Erythrosine (FD & C Red No. 3) is an iodine-containing food colour which was used as an example in the application of the proposed approach of data-derived safety factors. The effect of erythrosine on the thyroid and the mechanism by which the effect is induced has been central to the discussion of the establishment of an Acceptable Daily Intake (ADI), or not, and a short account is given of the effect of erythrosine on the thyroid. The evaluation of erythrosine as a secondary tumorigenic agent was based on the evaluations of the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and the Scientific Committee for Food of the Commission of the European Communities (SCF). In the proposed decision tree scheme, three different possibilities were examined. One was based on the long-term data and the second on the hormone data in the rat; the third was based on the NOEL for hormonal changes in humans. The three approaches with different NOEL and default values resulted in the following ADIs: 0.25, 0.3 and 0.1 mg/kg bw. The cases are discussed and it is concluded that the ADI based on the NOEL in human studies seems most appropriate. As there is most uncertainty about the default value for human pharmacokinetic variability, it is suggested that further human studies might elucidate this point.