Analysis of 100 patients receiving HLA identical sibling transplants was performed. Excellent graft survival demonstrated in the group attests to the importance of matching serological determined antigens. There seems to he a modest beneficial effect on antilymphoblast globulin in low dosage, but not in high doses. Insulin dependent diabetes mellitus results in a significant negative influence on patient survival and graft function in the male recipient but not in the female. A particularly striking point that emerges is the potential hazard in incorrectly treating for rejection. Rejection occurs very rarely in these patients; in a patient with deteriorating renal function, etiologies other than rejection should be vigorously sought (including trans-cutaneous biopsy) prior to initiation of rejection therapy.