Abstract The influence of a synthetic antifibrinolytic agent, tranexamic acid, on the tissue fibrinolysis of the rat lung was studied and estimated semiquantitatively by a histochemical technique modified from Todd. Tranexamic acid, administered iv to rats in doses from 5 to 100 mg/100 g of body weight, was found to decrease the tissue fibrinolysis. The maximum decrease of fibrinolysis was seen 5–15 min after iv administration of tranexamic acid. A retention of tranexamic acid in the lung tissue and probably in the lung vessel endothelium was observed. This might be of importance for the local inhibitory action of tranexamic acid on tissue fibrinolysis.