In order to find early indicators of kidney transplant rejection before clinical symptoms were noticed, parameters of the coagulation, fibrinolytic and kallikrein-kinin systems were measured. Nineteen patients were followed before and daily after kidney transplantation during the first week and every second day in the following weeks. All patients received immunosuppressive therapy with cyclosporin and corticoids. Ten patients suffered from transplant rejection. The first rejection occurred on the 7th day after transplantation. Of all the parameters measured, kallikrein inhibition, beta-FXIIa inhibition, plasminogen and antithrombin III were early indicators of kidney transplant rejections. A rise in these parameters could be demonstrated 2-3 days before clinical signs were noticed. In the other 9 patients no significant rises in antithrombin III, plasminogen, kallikrein inhibition and beta-FXIIa inhibition could be found.