In 45 recipients of intrafamilial kidney transplants, the one year survival of sibling grafts was 95% and of parental grafts 71%. HL-A compatible grafts had a one year survival of 94% compared to 75% of HL-A incompatible grafts. At the same time, the survival of MLC compatible grafts was 100% and that of MLC incompatible grafts 74%. These differences are not statistically significant but suggest a prognostic importance of MLC, as well as HL-A matching. MLC compatibility might be more crucial than HL-A compatibility. MLC test performed after transplantation when the recipients were on maintenance immunosuppressive therapy, did not show reduced reactivity of recipient lymphocytes as compared to tests performed prior to surgery.