Pharmacological blockade of fibroblastic proliferation after glaucoma filtration surgery by using antimitotic agents in different formulations (liposomes, nanospheres) is of great clinical interest. However, only limited comparative data are available on the effect of encapsulated drugs on intraocular pressure (IOP) after filtering surgery. Therefore we have studied the effect on IOP of liposomes, nanospheres and a solution of mitoxantrone (MTO), a well-known antimitotic, in rabbits before and after sclerectomy. MTO in solution form, as well as in a liposome formulation, improved the outcome of the surgery by reducing IOP when administered subconjunctivally just following surgery. This effect was similar to mitomycin-C application. In contrast, neither prior administration nor subconjunctival nanosphere injections induced a reduction in IOP. Liposome administration demonstrated no delayed action or promoting effect but reduced the occurrence of corneal opacity observed in groups treated with MTO in solution.