Abstract: In order to study whether Demodex folliculorum(D. F.) is a pathogenic factor of rosacea we have observed the results of 100 casks in the papular and pustular,stages treated with metronidazolum.Prior to treatment, all the patients: were examined for D. F, in the content of the nasal. sebaceous gland and facial pustule. 93 cases showed positive D. F. in the content of nasal sebaceous gland, 87 of them showed concurrent positive D. F. is the contest of facial pustule,No D. F, was,found in the nasal sebaceous gland and,facial pustule of the remaining 7 cases. After treatment for 2-4 weeks, both the D. F.Positive and D. F. negative cases showed the same good therapeutic effect. In all the clinically cured cases, those who showed positive D. F, before treatmeat remained positive and the D. F.found were still alive. Thus rosacea is not caused by D.F.