The monographs in this volume summarize data on the veterinary drug residues that were evaluated toxicologically by the Committee: the antimicrobial agents colistin and erythromycin. For the third antimicrobial agent, tylosin, a toxicological monograph has not been prepared. No data were submitted, and a brief review of the tocicological information available in the scientific peer-reviewed literature did not allow an evaluation of the compound.This volume and others in the "WHO Food Additives Series" contain information that is useful to those who produce and use food additives and veterinary drugs and those involved with controlling contaminants in food, government, and food regulatory officers, industrial testing laboratories, toxicological laboratories and universities.