Transmission of infection to recipients of solid organs is uncommon but well documented. Improved technologies for the diagnosis of infectious diseases suggest possible changes to paradigms used in the screening of organ donors to prevent disease transmission with transplantation. Available microbiologic assays, including molecular tests, are generally designed for use as diagnostic tools in individuals believed to have a specific infection based on clinical or epidemiological criteria. By contrast, these assays often lack the performance characteristics required for screening of deceased organ donors. This challenge is apparent with the analysis of assays for human T-cell lymphotropic virus-I and -II in low-risk populations. Changing epidemiologic patterns associated with the spread of novel pathogens or altered patterns of immigration will necessitate flexibility in the "list" of potential pathogens. Individual benefits from transplantation generally outweigh the risk of transmission of infection. However, this favorable experience will not obviate the need to continuously improve screening practices.