In the clinic of renal transplantation the difference of histocompatibility matching is significant in judging the prognosis of renal transplantation. MLC test is one of the histocompatibility tests indispensable to select donor-recipient combination, but generally it takes as long as 4-6 days, and it is not easy to use as routine for the practice of urgent renal transplantation. In this study, for the purpose of clinical application of cadaver renal transplantation on the basis of protein synthesis rate with (3)H-leucine pulse label method, this method was used to conduct technical basic experiment for rapid MLC test. First in establishing the condition of culture, Eagle's MEM was used which contains no leucine in the culture, and human serum was not added. The maximum number of reacting lymphocytes in MLC test was 1×10(6)/0.2ml/well. At 24 hours after commencement of culture % SPS (stimulation of protein synthesis) became maximum, and it was decided as time of judgement. There was correlation between rapid and standard MLC tests. % SPS of 10 cases of living donor transplantation was 11.8±16.7, % SPS of 10 cases of cadaver donor transplantation 97.6±31.5, and there was a significant difference (p<0.001). About 9 cases of cadaver kidney transplantation, low HLA matching grade showed high % SPS and a tendency of bad renal function after transplantation. In the cases whose renal function was lost within 3 months after transplantation % SPS tended to be higher than in the cases whose transplanted kidney survived longer. Although there are many factors which influence the prognosis of renal transplantation, it has been suggested that at least such a combination should be selected as % SPS below 80 and HLA matching above 2 matched to maintain good renal function for a long time. From the above, this rapid MLC test has been recognized retrospectively useful to test histocompatibility matching of urgent cadaver renal transplantation.