The method of cluster analysis was used to examine the data of Wraith, Cunnington & Seymour (1979) to assess the role and allergenic importance of storage mites in house dust and other environments in relation to certain factors thought to influence patients' exposure to these species. The analysis provided strong statistical evidence that (a) excessively damp housing and (b) occupational risks of exposure were the two main factors associated with allergy to these species. It also indicated that sensitivity to D. pteronyssinus remained unaltered in environmental conditions more favourable to the growth and development of storage mites. Furthermore, it was shown that the storage species form a group of similar allergens distinct from the house-dust mite.