Legally, zero tolerance applies to all residues of MG and LMG in foodstuffs as MG is not registered for use with food producing animals worldwide. Nevertheless, consumers are exposed to residues of MG as demonstrated by frequent detects of MG residues in fish and fish products that may be due to illegal use but maybe also derive from additional environmental sources. In the EU, a legally non-binding “minimum required performance limit” (MRPL) of 2 µg/kg has been set as action limit for internationally traded food consignments. But technical feasibility alone and not potential health risks is the yardstick for the establishment of a MRPL which has never as a rule undergone a risk assessment! Thus, current data suggests that MG and especially LMG may be carcinogenic and also provided some evidence that they are in vivo mutagens. Information on practical importance and multiple uses and residue data from supervised trials conducted according to Good Veterinary Practice (uptake, distribution, bioaccumulation, interspecies variations) and on possible environmental back­ground contamination is missing. Such data is currently produced in terms of two research studies and will be presented together with different approaches for a holistic risk assessment applying concepts based on a margin of exposure or a threshold of toxicological concern.