In a survey of the mite fauna in 30 homes in Oxfordshire, Dermatophagoides pteronyssinus and Euroglyphus maynei were found to be the most abundant species but D. farinae was absent. Of a total of 14 parameters investigated for their influence on mite numbers, relative humidity was apparently the most important factor. Bedrooms with humidities above 64% contained significantly more mites in mattresses than those with lower humidities. Bedroom humidity and thus mattress mite numbers were apparently related and were influenced by the bedroom minimum temperature, the age of the house and the use of central heating. These trends were not seen in the numbers of mites found in living-room carpets. Atopic and non-atopic participants involved in this study did not differ significantly in the numbers of mites found in their homes.