Extensive research in xenotransplantation is being propelled by the critical shortage of allotransplants. About a third of the patients on organ waiting lists in the United States die for lack of available organs, and in the United Kingdom fewer than 30% of those waiting for kidneys receive them each year.1^–3 The human toll of suffering in patients who need transplants is great, and their quality of life is poor.

This update focuses on whole organ xenotransplants. It draws on the latest published studies and the assessments at two recent meetings—a conference of US and UK scientists, ethicists, and policy experts in New York in May 1999, and the June 1999 meeting of the xenotransplantation subcommittee of the US Food and Drug Administration's Center for Biologics Evaluation and Research.

Research is currently being conducted in all the critical areas of xenotransplantation, and this will, it is hoped, make xenotransplants safe and effective for human beings. These critical areas include immunological barriers, physiological functioning, infectious disease risks, and pivotal ethical issues.