Background. Mite allergen levels vary enormously between different homes in the same geographical area. No large scale studies of mite levels in Manchester homes has been conducted to identify factors associated with higher levels. Objectives. To quantify exposure to mite allergens and to identify characteristics associated with higher Der p 1 levels in a large sample of homes in Manchester, UK. Methods. Der p 1 was measured in dust from the living room floor, sofa, bedroom floor and mattress in 564 homes. Data on household characteristics were collected by administering a questionnaire. Univariate and multivariate analyses were performed to identify household characteristics associated with higher mite allergen levels. Results. Der p 1 levels were highest in the mattress (GM 1.19 gg/g, 95% CI 0.98-1.45, P <0.001). Two-thirds of homes contained Der p 1 levels > 2 μg/g in at least one dust reservoir, and 40.3% contained Der p 1 greater than 10 μg/g. There was a large range in Der p 1 levels between homes (> 103-fold). Damp and condensation were common findings in homes. In the multivariate analyses, factors associated with higher Der p 1 levels in more than one dust reservoir were older homes, older living room carpets, damp, condensation and mixed glazing. Older mattresses were associated with higher mite allergen levels in the mattress where the age of the mattress was recorded. Twenty-four homes contained no detectable mite allergen, six of which reported damp. Conclusions. Mite allergen levels are high enough in two of every three homes to be associated with an increase in the risk of sensitization to mite. Factors such as older homes, carpets and mattresses, damp and condensation are associated with higher mite allergen. However, mite allergen levels are occasionally unpredictably very low in homes with risk factors for high levels.