The histopathologic and cytopathologic study of ocular fluids obtained for diagnostic purposes is presented. The analysis of fluid specimens with millipore filter, celloidin bag-cell block, and transmission electron microscopy techniques has proved to be effective for establishing and confirming clinical diagnoses. Diagnostic vitrectomy can be readily used to evaluate such conditions as intraocular tumors, lens and blood-induced glaucoma, inflammatory conditions, amyloidosis, persistent hyperplastic primary vitreous (PHPV), epithelial ingrowth, and tractional vitreoretinal membranes.