Antimicrobial drugs are fed to animals at low levels to treat diseases, to promote growth, and to increase feed efficiency. Incorporating low levels of antimicrobial drugs in livestock feeds has been shown to be a factor stimulating the development of antimicrobial drug resistant bacteria in livestock. Since many of the drugs used to treat livestock are the same as or are related to drugs used in human health care, there is concern that resistant organisms may pass from animals to humans through the handling of animals or food derived from animals. The movement of pathogens from animals to humans, and vice versa, has been documented, but the extent to which it has occurred or could occur is unknown. Although it is estimated that as little as 10 percent of the problems of drug-resistant pathogens in humans originate in livestock health care practices, there is currently considerable debate about the frequency and costs of human disease outbreaks resulting from animals infected with drug-resistant pathogens. Several European countries have banned the growth-promoting use of antimicrobial drugs in livestock production as a precautionary measure to prevent resistant organisms from passing from animals to humans. This report presents preliminary estimates suggesting that discontinuing the use of antimicrobial drugs in hog production would initially decrease feed efficiency, raise feed costs, reduce production, and raise prices to consumers. Longer term effects were not examined.