In studies on the fibrinolytic system in human tears, we examined the species and activity of plasminogen activator (PA). In fibrinolysis enzymography, the lytic bands and molecular weights of 64 and 52 kDa, on the fibrin-agarose detector membrane. The dissolved band of 64 kDa was quenched by adding antihuman tissue type-PA (t-PA) IgG to the fibrin-agarose detector membrane, and that of the 52 kDa band was quenched by adding anti-human urokinase type PA (u-PA) IgG. In reverse fibrinolysis enzymography, no inhibitory activity to PA or plasmin was observed on the fibrin-agarose membrane. These findings suggested that t-PA and u-PA coexist and that the PA inhibitor is scanty in human tears. We estimated the fibrinolytic activities of t-PA and u-PA respectively, using anti-human u-PA and t-PA IgG by amidolytic assay. Fibrinolytic activity of t-PA in human tears was 5.2 +/- 1.3 I.U. ml-1 (n = 6), and that of u-PA was 2.8 +/- 0.5 I.U. ml-1 (n = 6). To investigate the origin of PA present in tears, we carried out Todd's fibrinolysis autography and immunohistochemical study. Localization of PA activity and t-PA antigen were confirmed in the corneal epithelial cells and the vascular endothelial cells of the conjunctival vessels. The corneal epithelium and conjunctival vessels may produce PA and play some part in the secretion of PA into tears.