Of the 320 cadaveric renal transplantations carried out between 1970 and 1978 in Stockholm 308 were analysed with respect to dependence of graft survival on HLA-A, -B matching. From November, 1973, kidneys with 3 or 4 HLA-A, -B incompatibilities were accepted much more often than had previously been the case. All but 7 of the 90 grafts with 3 or 4 incompatibilities were transplanted during that period. In order to obtain as homogeneous a group as possible the transplantations performed during this period were analysed separately, and transplantation performed on diabetic patients and retransplantations were excluded. This material comprising 141 transplantations was examined also with respect to other factors that may have a bearing on graft survival. As regards the factors mean age, pre-transplantation dialysis and blood transfusions, primary diuresis at transplantation and high-dose ALG therapy there was no essential difference between the recipients of kidneys from donors with 1 or 2 HLA-A, -B incompatibilities and the 3 or 4 incompatibility group. Thirteen of the 141 transplantations were fully compatible but because this group was small it was not included in the statistical analysis. After 2 years the group with 3 or 4 HLA-A, -B incompatibilities displayed a significantly poorer graft survival than the one with 1 or 2 incompatibilities (p less than 0.05).