Within four decades, transplantation of the kidney, and more recently of other organs, has become a unique and exciting treatment for patients with end-stage organ failure; indeed, in 1989 over 14,000 individuals received allografts in the United States alone (1). The results have progressively improved secondary to refinements in tissue typing, greater understanding of patient physiology, better surgical and perioperative techniques, and more effective immunosuppressive modalities with coincident appreciation of their risks. At the same time, however, it has become clear that a significant proportion of grafts falter and fail within the first several months or years after placement, primarily because of progressive and irreversible host immunological attack despite continued administration of maintenance suppression. This persistent attrition of functioning allografts has been noted in analyses of several large col-lected series as well as in the results of individual units (2–6). Indeed, the rate of decline of long-functioning grafts has not changed over time regardless of improved immunosuppression; the curves have merely been pushed upward (2). In multicenter data from North America reported in 1988, less than half the renal allografts from cadaver donors continue to function at six years despite 80% behaving satisfactorily at the end of the first year; figures from the ongoing European Multi-center Trial show comparable trends (7). The rate of decline of other organ grafts are relatively similar: the incidence of coronary arteriosclerosis in heart grafts reaches 50% before five years leading to a 25% mortality rate (6, 8); the somewhat lower rate of chronic rejection of liver allografts (50–60% functioning at 5 years) may attest to the putatively lower immunogenicity of this tissue (9). Accruing data on the eventual survival of other organ grafts are sparse although the same trends seem evident. Thus, as a long-term answer to an irreversible disease process, organ transplantation has not yet lived up to its potential; chronic rejection–that ill understood process leading to the bulk of late graft failures–is inexorable, undefined, and as yet uncontrollable.