A survey of dust samples from dwellings, hospitals and some public utilities (libraries, institutes) in several Upper Silesian towns was undertaken to determine the prevalence, number and species of mites. Total seasonal dynamics of dust mite species of the family Pyroglyphidae in dust from beds, floors/carpets and upholstery furniture in dwellings was analysed. Over a 4-years period, 402 dust samples were studied: 238 samples from dwellings, 122 samples from hospitals, 14 from libraries and 28 from institutes. Mites were present in 51.3%, 50.0%, 21.3% and 17.9% of dust samples from dwellings, libraries, hospitals and institutes, respectively. Generally, they were found in 160 samples (39.8%) out of 402 examined. The majority of mites (96.0%) were found in samples from the dwellings, especially in dust from upholstery furniture, couches, sofas and beds. More than 30 mite species were found of which the most abundant and common were pyroglyphids, especially Dermatophagoides pteronyssinus and D. farinae. The pyroglyphid mites constituted 89.2%, 78.9% and 57.5% of a total count of mites collected from dwellings, libraries and hospitals, respectively, and were not found in institutes. D. pteronyssinus was the dominant, especially in libraries and hospitals, however, in dwellings D. farinae was more abundant per 1 gram of dust as the former species. Another pyroglyphid mite, Euroglyphus maynei, occurred in very small numbers. The highest mite densities per gram of dust were noted in dwellings and libraries. A mean number of mites per 1 gram of dust from dwellings was 73.7 +/- 182.9 (range 1.0 - 1560.0), whereas mean values of indoor relative humidity and temperature were 64.5% RH and 22.7 degreesC, respectively. The low mean indoor relative humidity of ambient air, resulted in the relatively low mite frequency (only about 51.3% of samples were positive for mites) and density detected in the dwellings.