L-arginine ahs received much attention in numerous aspects of the regulation of vascular tone and haemostasis. L-arginine seems to be capable to bind to plasminogen, too. The aim of the present paper is to investigate the action of L-arginine on in vitro plasmin generation and fibrino(geno)lysis by chromogenic, kinetic plasmin generation assay and electrophoretic analysis. The acceleration of tPA-induced plasmin generation in the presence of low concentration of L-arginine, along with augmentation of in vitro fibrinogenolysis have been documented. L-arginine may have a role in the modification of fibrinogenolysis, and this role should be considered if arginine is used as an element of some novel antithrombotic agents.