Preliminary retrospective studies of tissue typing in man were based upon comparison of lymphocyte antigens of chronic survivors with their donors after renal homotransplantation. 1–3 In the last report3 a statistically significant association was demonstrated between the excellence of the late clinical outcome and the donor-recipient compatibilities in the leukocyte groups tested. These initial efforts to establish the relationship between the antigens under analysis and human histocompatibility factors were not altogether satisfactory, however, since they involved solely retrospective observations on patients long after operation. These studies of surviving recipients and their donors excluded the early failures from consideration. Furthermore, although a correlation existed in the chronic survivors between the excellence of antigenic match and the benignancy of their course, several patients with mediocre matches had achieved good long-term results. Conversely, some patients with apparently good matches had developed late problems. 2

Nevertheless, the results were sufficiently encouraging to warrant a trial of prospective matching. This has been carried out in 32 patients treated from October 12, 1964 to October 12, 1965. In each instance, the donors were selected in Los Angeles on the basis of the best available match, either from a related or nonrelated population. Transplantation was subsequently carried out either at the Colorado General Hospital or the Denver Veterans Administration Hospital. The collaboration provided certain advantages for evaluation of the results. First, the surgical and medical practices in the Denver institutions were relatively well standardized. In addition, the results obtained with 64 previous cases in which the donor and recipient were randomly selected4 were available for comparison. Finally, all available pathologic material in the original unselected series had been examined by KA Porter, making possible a histopathologic correlation between the failures in the original nonselected group and those of the present studies.