Abstract: The invention relates to the production of biologically active recombinant human and animal urokinases involving construction and expression of recombinant expression constructs comprising coding sequences of human or animal urokinases in a plant expression system. The plant expression system provides for post-translational modification and processing to produce a recombinant gene product exhibiting biological activity. The invention is demonstrated by working examples in which transgenic tobacco plants having recombinant expression constructs comprising human urokinase and urokinase nucleotide sequences produced biologically active urokinase. The recombinant urokinases produced in accordance with the invention may be used for a variety of purposes, including but not limited to thrombolytic therapy and clearing catheters.