According to the latest reports Demodex mites appear to play an important role in the pathogenesis of chronic blepharitis. Demodex mites are cosmopolitan and are present in many species of mammals. In this paper we describe two species that are found in humans: Demodex folliculorum and D. brevis . Infection occurs during direct contact with an affected person and also through contact with dust containing eggs of the parasite, through contact with bed linen, as well as cosmetics used together with an affected person. Treatment of chronic blepharitis caused by D. folliculorum and D. brevis is difficult and time consuming. Some improvement can be achieved after topical application of yellow mercury ointment, sulphuric ointment, camphor oil, crotamiton, cholinesterase inhibitors, sulfacetamide, steroids, antibiotics and antifungal drugs. Good results have been achieved with oral ivermectin and permethrin cream. However, the best results were observed after treatment with metronidazole.