Many genes derived from plant RNA viruses expressed in transgenic plants confer resistance against infection by viruses that were the original source of the genes and in some cases, by other viruses as well. As of March 17, 1995, over 240 field tests of virus-resistant transgenic plants had been conducted in the United States. Recently, the first virus-resistant transgenic plant (ZW 20 squash developed by Asgrow Seed Company) was approved by the U.S. Department of Agriculture (USDA) for widespread commercial production. Other virus-resistant plants are likely to be commercialized by the turn of the century. Although the use of viral genes for resistance to plant viruses has many potential benefits, some risk issues associated with the use of these genes have been raised.The principal issues are associated with the possibility that recombination between an infecting plant RNA virus and a viral RNA produced from a transgene will result in a new, problematic virus. Additional issues include potential synergism, transcapsidation, and other interactions that might lead to new or more severe disease problems. To address these issues, the USDA's Animal and Plant Health Inspection Service (APHIS) and the American Institute of Biological Sciences (AIBS) convened a two-day work-shop (Appendix A) on April 20-21, 1995, in Beltsville, Maryland. Workshop participants included virologists and others with expertise in molecular biology and plant pathology (Appendix B). Support was provided by APHIS and by the Biotechnology Industry Organization. With assistance from the program committee (Appendix C), APHIS developed a list of 18 questions related to the potential risks of transgenic virus resistance. The questions were categorized as follows: Recombination and Mixed Infections; Transgenes; Experiments; and Benefits and Post-Commercialization Monitoring. To provide a context for answering the questions, formal presentations were given by leading virologists on resistance mediated by viral coat proteins, movement proteins, replicases, and RNA, as well as presentations on transgenic complementation, recombination, synergism, and replication. Issues concerning the potential effect of gene flow of transgenes to wild plant populations were not addressed. After the formal presentations, the workshop participants broke into five groups according to their interests. There were two groups for coat protein, one group for replicase, one group for movement protein, and one group to cover other viral genes. Each group was asked to address the 18 questions in terms of their group's gene assignment.