Demodex is a mite commonly found in eyelash hair follicles and sebaceous glands of healthy people. Due to the fact this mite has also been reported in many chronic cases of blepharitis, we aimed to investigate the incidence of infestation with this mite in healthy people and in patients with chronic blepharitis, in addition to evaluating the response to the different treatments used for blepharitis.105 subjects without blepharitis were selected as a control group and 20 subjects diagnosed as having chronic blepharitis were selected as patients. Epilated eyelashes were observed under microscope in both groups of patients. Those with overpopulation of mites were treated with ether lid and eyelash scrubs and 2% mercury oxide ointment.The incidence of Demodex infestation in the control group was 0.08 mites per eyelash, whereas in the patients with chronic blepharitis the incidence was 0.69 mites per eyelash; this difference was statistically significant (p=0.006). All the mites found were Demodex folliculorum except in one patient where the mite was identified as Demodex brevis. After 3-8 weeks of specific treatment the number of mites per eyelash decreased dramatically (0.03, with p=0.001). Two patients were intolerant of the therapy.In this study the incidence of Demodex in patients with blepharitis was very high, when compared with normal subjects, showing a clear association between blepharitis and Demodex infestation. Treatment with mercury oxide ointment was satisfactory in controlling the infection, despite difficulty in its application and occasional toxicity.