Clinical trials of xenotransplantation: waiver of the right to withdraw from a clinical trial should be required.

Xenotransplantation pits clinical research ethics against public health needs because recipients must undergo long-term, perhaps life-long, surveillance for infectious diseases. This surveillance requirement is effectively an abrogation of the right to withdraw from a clinical trial. Ulysses contracts, which are advance directives for future care, may be an ethical mechanism by which to balance public health needs against limitation of individual rights.