1. Among patients transplanted in 93 selected centers with good follow-up data, the 10-year graft survival of first cadaver-donor transplants was 18%, parental donor grafts 39%, and HLA-identical sibling donor grafts 66%. The respective half-lives were 6.8, 10.8, and 24.5 years. The donor relationship has been the most important factor in long-term success. 2. Patient half-life for recipients younger than 16 was 36 years; for recipients 16-50 years old it was 17.6 years, and for those over age 50, it was 10.4 years. This marked difference in patient half-lives severely affected functional graft half-lives for the 3 age groups; 6.8, 10.3, and 16.7 years, respectively. However, the differences in patient survival for the 3 age groups were not significantly reflected in graft half-lives that were 6.8, 7.7, and 6.5 years, respectively. Thus, graft loss resulting from rejection was significantly lower in older than in younger patients. 3. Cadaver-donor kidneys with cold ischemia time up to 12 hours and half-lives of 9.1 years in transplants performed before 1975, compared to half-lives of 6.4 years for those with more than 24 hours cold ischemia time. In transplants performed between 1980 and 1983, the half-life of kidneys with cold ischemia time up to 12 hours was 8.7 years, compared to 6.9 years for those with more than 24 hours cold ischemia time. The long-term effect of cold ischemia persists but has diminished in recent years. 4. HLA-A,B loci matching had a significant effect on long-term graft survival. The 10-year graft survival of A,B matched grafts was 30% compared to 18% for 3 or 4 HLA-A,B mismatched transplants. This difference increased at 15 years to 25% in the matched grafts and 10% in the mismatched grafts. 5. A very strong recipient race effect was evidenced by the 24% 10-year graft survival in Whites compared to 10% in Blacks. The half-lives were 8.2 in Whites and 4.8 in Blacks. 6. A listing of 15-year graft survivors has been compiled according to transplantation centers. There was a total of 969 from cadaver donors, 283 from parental donors, and 457 from sibling donors. 7. An analysis of the characteristics of the 15-year graft survivors showed a preponderance of patients with favorable factors, noted in the analysis above. As might be expected, the most striking was the fact that 27% of the 15-year survivors had received kidneys from sibling donors, despite the fact that such donors comprised only 17% of those transplanted in the pre-1975 era.