A wide range of antimicrobial drugs, covering a number of therapeutic classes, is used in the treatment of animal diseases. The majority of these drugs have low toxicity but some may induce idiosyncratic reactions in humans, and some of these are potentially fatal. Occupational exposure to some of these during veterinary use has resulted in respiratory effects and skin reactions. The drug tilmicosin has led to fatalities after accidental self-injection. However, the major concern arises from residues of antimicrobial drugs in food derived from treated animals. To assuage fears over adverse events arising from residues, many of these drugs have been evaluated for their safety to consumers and in the European Union, maximum residue limits have been established for many of these agents. However, some drugs are considered too toxic to permit the establishment of maximum residue limits, including chloramphenicol and the nitrofurans. The major aspects of the toxicity of the antimicrobial drugs are reviewed in this chapter and the implications for occupational safety and consumer exposure are discussed.