Organ transplantation in the 1960s proceeded according to a "lifeboat" ethics formula with physicians acting as "gatekeepers." Selection of transplant recipients is now based on medical urgency and waiting time. Some candidates continue to be given low priority by virtue of psychological impairment. The three As--advanced age, acquired immune deficiency syndrome (or positive human immunodeficiency virus status), and alcoholism--also stand out as characteristics that tend to exclude candidates. Cancer is another relative or absolute contraindication to transplantation. This article focuses retrospectively on the psychosocial and medical aspects of the decision to include six patients at Massachusetts General Hospital who were selected for organ transplantation despite their borderline candidacy. The authors introduce four lines of thinking that decision-makers might use to either include or exclude marginal candidates (e.g., the physician's interpretation of what duty requires, the patient's or surrogate's wishes, cost-benefit considerations, or the need for research to improve our scientific understanding of transplantation issues) and discuss an ethical approach that supports each line of thinking. The authors conclude that not all of the ethical approaches lead practitioners and policymakers to the same conclusions regarding the optimum size of or who should be a part of the recipient pool. The future of who receives transplants and why depends at least in part on the underlying ethical considerations that are deemed appropriate as determinants of practice and policy.