It has been reported that a decrease in cellular immunity occurs and a serum immunosuppressive factor exists in uremic patients. In this study, we attempted to examine the change in cellular immunity after renal transplantation, the serum immunosuppressive factor and the usefullness of mitogenic blastogenesis for immunological monitoring. Peripheral blood lymphocytes were isolated by the Ficoll-Conray gradient from 10ml of fresh heparinized blood obtained from renal allograft recipients and healthy individuals. Serum was isolated from 10ml of fresh nonheparinized blood and added in culture after inactivation and sterilization. Pooled AB serum was used for control. Lymphocytes were adjusted to a concentration of 5 x 10(5)/ml in RPMI, supplemented with 60μg/ml Kanamycin and 20% patient's serum or AB serum, and then to 200μl of this suspension, phytohemaggultinin, pokeweed mitogen and concanavalin A were dispensed. The culture was incubated for 72hrs in a humidified atomosphere of 5% C0(2) and air, after which 1μCi tritiated thymidine was added to each well and the incubation continued for 24hrs. The contents of each well were transfered to glassfiber filters, and the amount of isotope incorporated was determined in a liquid scintillation counter. PHA and PWM blastogenesis of patients treated with hemodialysis were significantly decreased. PHA, PWM and Con A blastogenesis of renal allograft patients were significantly decreased, but turned to recover 1 year after renal transplantation. Sera of renal allograft patients suppressed all kinds of blastogenesis of healthy individuals, but only PHA and PWM blastogenesis of renal allograft patients themselves. In renal allograft patients with good renal function 1 year after transplantation, Con A autosuppression was very weak and negative suppression increased significantly. There were correlations between preoperative PHA blastogenesis and acute rejection, and between postoperative PWM blastogenesis and chronic rejection. From these findings, it is concluded that clear elavation of PHA, PWM blastogenesis and suppression of Con A blastogenesis are slightly usefull for immunological monitoring of acute and chronic rejection.