The following questions were asked to the Scientific Committee on the presence of endogenous anabolic and/or prohibited substances in food-producing animals: - Question 1: Among the substances being examined by the FASFC, which are those whose presence in a matrix of animal origin is suspected to have an endogenous origin (metabolism, feed, .)? - Question 2: In which matrices and in which animal species (categories), the presence of substances of endogenous origin can be observed? o Can a residue concentration be determined differentiating an endogenous origin from an illegal treatment for combinations substance/matrix/species? - Question 3: Can the presence of prednisolone and thiouracil in matrices other than urine also have an endogenous origin? o If this is the case, can a residue concentration be determined which can differentiate the origin (endogenous versus illegal treatment) for combinations of substance/matrix/species? ; BE; fr; secretariaat.scicom@favv-afsca.be