Use of antimicrobics has increased in both human and veterinary medicine. This is due in part to the availability of the antimicrobics and the efficacy they impart in control of certain infectious diseases. However, use of antimicrobics can lead to the development of resistance to the antirnicrobics. Antimicrobial resistance can diminish effectiveness and may even render an antimicrobic ineffective as a therapeutic. Although use may result in a portion of bacteria that are resistant, the exact fate of this population in terms of persistence and transmission has been difficult to determine. Use panerns in veterinary medicine (therapeutic versus preventive versus growth promotion use) also complicates the picture. Additionally, while transmission of resistant bacteria from animals to humans occurs, it has been difficult to assess the extent to which this occurs and the impact transmission has on actual dissemination of resistant populations.