Patients frequently develop nosocomial infections that are caused by normal flora colonizing the patient at the time of admission, or by exogenous pathogens that are acquired and subsequently colonize the patient after admission to the hospital. To prevent nosocomial infections, a variety of strategies have been used either to prevent colonization from occurring, to eradicate colonizing organisms, or to prevent the progression from colonization to infection. These strategies include implementation of infection control measures designed to prevent acquisition of exogenous pathogens, eradication of exogenous pathogens from patients or personnel who have become colonized, suppression of normal flora, prevention of colonizing flora from entering sterile body sites during invasive procedures, microbial interference therapy, immunization of high-risk patients, and modification of antibiotic utilization practices. Because strategies that require widespread use of antimicrobial agents to suppress or eradicate colonizing organisms tend to promote emergence of multidrug-resistant pathogens, greater emphasis should be given to those strategies that prevent colonization from occurring or employ techniques other than administration of prophylactic antibiotics to eradicate colonization. Restricting inappropriate use of antibiotics should reduce the frequency with which patients become colonized and infected with multidrug-resistant organisms.