||In this study, we utilized the BmNPV to express active human tissue plasminogen activator, a potent fibrinolytic agent, in BmN cells and the silkworm Bombyx mori. Two expression vectors, one containing the original t-PA cDNA and the other a mutated t-PA cDNA, were constructed. The BmLSP signal peptide was used to replace the original t-PA signal peptide, and a short sequence containing 7 bases, TATAAAT, was added immediately before the signal peptide. Recombinant viruses were generated from these vectors, and were used to infect BmN cells. Media from a titne course experiment of 5 days were studied. The radial caseinolysis assay was employed to check the activities of the expressed products. This study gave positive indication that human t-PA could be expressed by the BmNPV system. It seemed that the mutation introduced into the t-PA gene did enhance the level of expression and secretion to a certain extent. However, more work need to be done on the characterization and the purification of the expressed products.