Microplasmin (Thrombogenics Ltd., Leuven, Belgium) is a recombinant molecule consisting of the catalytic domain of human plasmin. It is highly characterized, and supplied in a stabilized form, simplifying storage and administration. Microplasmin shares the same catalytic properties like human plasmin, but it is much more stable compared to plasmin. It has been shown previously that both plasmin and microplasmin are capable of inducing PVD. This chapter focuses on one of the most promising current concepts of pharmacologic vitreolysis, i.e. microplasmin-assisted vitrectomy. We report on the preclinical work of plasmin and microplasmin which lead to the clinical investigation of microplasmin in different clinical trials, the so-called MIVI trials.