The immunological in vitro responses of cadaver kidney transplanted patients against donor specific target cells were investigated with the test systems for antibody-dependent cell-mediated cytotoxicity (ADCC) and direct cell-mediated cytotoxicity (DCMC). The test systems were used in 58 recipients just before the transplantation. Nine recipients (17%) had positive donor directed ADCC reactivity and of these seven had early rejection episodes, but this outcome was not significantly different from the outcome in the ADCC negative group. Only one recipient showed positive donor directed DCMC reactivity and had early loss of the graft in rejection. The test systems were further used to monitor the donor specific responces after the transplantation in 32 recipients. Positive DCMC reactivities were significantly correlated with clinical rejections but most often positive reactions occurred too late to be of predictive value. The donor specific ADCC reactivity after transplantation was not clearly correlated with rejections. It is concluded that the predictive and diagnostic values of the two test systems were too weak to justify their use as routine methods in the clinical management of the kidney transplanted patient.