Abstract: There is provided a process for the production of pure, concentrated urokinase starting from a crude urokinase solution. The crude urokinase solution is contacted in a medium having a pH of .gtoreq.6 with a porous solid matrix having a high specific surface area on whose surface there is immobilized aprotinin. Subsequently the urokinase adsorbed in this manner is eluted in an elution agent having a pH.ltoreq.4.5. There are obtained highly concentrated and very pure solutions of urokinase. The urokinase is used in medicine as a pharmaceutical for the dissolving of fibrinous clots and coagulums.