The parameters of kallikrein-kinin system (KKS) in the renal graft tissue (the cortex and medulla) and urine in 10 rats were investigated 4, 8 and 12 days after transplantation prior to the clinical symptoms of graft rejection. Controllable activation of a kinin-generative link of KKS (more pronounced in the medulla than in the cortex) is found. It manifests itself in growth of the kallikrein activity (in proportion to terms of transplantation) and in an increase of the inhibitor level. Kininase activity is observed to be the highest on the 4th day, in the medulla the degree of increase being higher than in the cortex. Esterolytic activity of urinary kallikrein is observed to decrease, while its proteolytic activity--to increase. The urinary inhibitory and kininase activities increase. The disturbances in renal graft KKS lead to the local vascular thrombosis, decrease in graft perfusion, worsening of its function and potentiation of graft destruction. The data show that kallikrein-kinin system takes part in pathogenesis of renal graft rejection playing a mediator role in the functional and structural changes.