Swine are expected to be utilized as xenograft donors for both whole-organ and cellular transplantation. In order to meet the criteria for regulatory guidelines, donor animals are going to have to be free of potential zoonoses and other complicating diseases. Screening of animals will have to include tests for viruses, bacteria, parasites, congenital defects, and other inapparent diseases such as neoplasia or metabolic dysfunctions. The term Specific-Pathogen-Free (SPF) swine is a proprietary designation in the U.S. that does not include screening for all appropriate organisms for xenotransplantation. A program for breeding animals as xenograft donors will have to be conducted in a biomedical research facility rather than a conventional farm setting. The research programs at such a facility should include serology, microbiology, necropsy, histology and parasitology. The use of sentinel animal monitoring in a research facility is one method to ensure compliance. It will be impossible to provide complete individual animal screening in a timely fashion prior to performing a xenograft transplant. Quality control measures need to ensure that there is a reasonable confidence that the donor tissue is appropriate for the procedure to be performed. It is suggested that a term such as xenograft-defined flora be used to designate the appropriate health status of donor animals rather than SPF in order to avoid confusion with existing standards.