An increasing range of antibacterial compounds is being used for nonclinical purposes, especially in the fields of animal husbandry and fish farming. As in human medicine, exposure to antibiotics has lead to the emergence of antibiotic-resistant bacteria in animal populations. The potential impact of antibiotic use in animals on human health and the management of clinical infections in humans is discussed in light of growing evidence to suggest that "new" resistance genes and multiresistant pathogens with increased pathogenicity are emerging in food animals as a direct consequence of antibiotic exposure.