Kidney transplantation with a living unrelated donor was performed in 13 patients. The donors comprised 10 spouses, 2 brothers-in-law and 1 stranger. All donor-recipient pairs were red blood cell compatible with a negative T cell crossmatch. Five patients underwent transplantation before 1984 without cyclosporine immunosuppression; the 1-year patient and graft survival rates in this group were 40% and 20%, respectively. Eight patients have undergone transplantation since 1985 with cyclosporine immunosuppression. The 1-year patient and graft survival rates in this group were 100% and 88%, respectively (p = 0.03). Currently, 6 patients in the latter group have a well functioning graft with serum creatinine levels of 1.2 to 2.0 mg./dl. (mean 1.5 mg./dl.) and with followup of 1 to 6 years (mean 2.9 years). Excellent graft survival results can now be achieved with living unrelated donors and their expanded use can provide an important additional source of organs for transplantation.