The relationship of blood group compatibility and splenectomy to duration of kidney transplant function has been studied in 565 transplants performed during the 3-year period prior to 1(5 March 19(55. The data were analyzed, using conventional life table methods. The following trends are suggested from analysis of data on the ABO, I) or Rh, and P blood group systems: (1) ABO incompatibility tends to increase the incidence of transplants which never function. The difference between the proportions of transplants functioning at various post-transplant intervals appears to be due to other genetic factors acting independently of the ABO blood group system. (2) Compatibility or incompatibility for the D or J\h blood group system does not appear to be related to initiation or duration of transplant function. (3) Incompatibility for the P blood group system seems to have no influence on initial transplant function, but limited data suggest the possibility of ft subsequent, decrease in duration of function. Splenectomy prior to or at time of transplantation had no influence on initiation of transplant function. There is some indication in recipients receiving a related kidney that splenectomy results in a higher proportion of transplants functioning up to 3 months post-transplant. After the initial 3-month period transplants appear to function in about the same proportions in both spleneetomizod and nonsplenectomized recipients.