In many uveitis cases a biopsy of ocular tissues can enable an exact diagnosis to be established, unnecessary additional examinations to be avoided, and an appropriate therapeutic regimen to be selected. In general, follicle biopsy is performed where sarcoidosis is suspected, keratocentesis in viral uveitis and toxoplasmosis, and vitreous biopsy in tentatively diagnosed primary intraocular lymphoma (reticulosarcoma) and bacterial or mycotic endophthalmitis.