The hair follicle mites (Acari, Demodecidae) are obligatory and specific parasites of mammals, important in human and veterinary medicine. The family is represented by more than 100 species worldwide and 30 in Poland, therein 11 species (and 3 subspecies) were discovered from 10 species of native rodents. Fifty two striped field mice Apodemus agrarius from eastern Pomerania (Poland) were examined in 2006-2007; the presence of mites was confirmed by the standard method of digesting skin fragments (from head, belly, groin, limbs, genital-anal region, neck and back). Two demodectic mites were found: Demodex agrarii and D. arvicolae--specifically the form D. a. apodemi, previously recorded in the wood mouse (Apodemus silvaticus). Demodex spp. were noted in 53.8% of the examined mice; D. arvicolae was the dominant species (prevalence 48.1%, mean intensity 12.5), whereas D. agrarii was found in only a few hosts (prevalence 13.5%, mean intensity 7.6); these mites were more frequently found in males. D. a. apodemi were found mainly in skin of head and very few in skin of genital-anal region. D. agrarii lives in the ducts of the auricular sebaceous gland, in which all its developmental stages have been found; it is precisely the specific habitat of D. agrarii that determines its large size and its strongly elongated shape.