Pretransplant tests necessary for kidney transplantation are HLA typing, mixed lymphocyte culture response (MLR), and direct crossmatch. HLA typing and MLR are closely related to graft survival rates. The significance of HLA matching is generally known. In our analysis of 25 living related kidney grafts, graft survival rate of two haplo identical donor transplants was 4/4 (100%), while that of one haplo identical donor transplant was 18/21 (85.7%). Acute rejection rate in the MLR low response group (S.I. less than or equal to 5) was 2/7 (28.6%), while that in the high response group (S.I. greater than 5) was 11/19 (57.9%). HLA typing and MLR are useful in selecting the most suitable recipient. In order to reduce the risk of hyperacute or accelerated graft rejection, T warm direct crossmatch is performed. Anti-T warm antibodies are mainly produced by blood transfusion. In our study of 239 hemodialysis patients, there were 31 patients with positive T warm (13.0%), the positive rate became higher in proportion to increases in blood transfusion. Recently, there have been reports of kidney transplants successfully performed across T warm-positive crossmatches due to IgM antibodies. We also investigated the immunoglobulin class. Not only pretransplant crossmatch but also posttransplant crossmatch is necessary. In the case of accelerated, acute or chronic rejection, anti-donor HLA antibodies are produced in patients' peripheral blood. Thus, the test of posttransplant anti-donor antibodies is useful for the early detection of rejection, its diagnosis, and index of the prognosis. The sensitivity of flow cytometry crossmatches was compared to standard cytotoxicity crossmatch. Titration studies indicate a 32-64 fold range of greater sensitivity than the cytotoxicity test.(ABSTRACT TRUNCATED AT 250 WORDS)