In asthma, it is uncertain whether there is an association between degrees of exposure to domestic allergens and asthma severity. The pattern of sensitivity and exposure to common indoor allergens was examined in subjects with differing asthma severity. Sensitivity to house dust mite, dog and cat allergen and exposure to Derp 1, Can f 1 and Fel d 1 were assessed by skin prick tests and settled dust analysis in 28 subjects with severe asthma and 28 age- and sex-matched subjects with mild asthma (two declined skin prick test). All severe asthmatic subjects had at least one positive skin test and 20 of the 28 subjects were positive to all three allergens. Fourteen of the 26 subjects with mild asthma who took skin prick tests were positive to at least one, and one of these subjects was positive to the three allergens tested. Except for bedroom Fel d 1, the proportion of severe asthmatics both sensitized and exposed to each allergen at each site was significantly greater than the proportion sensitized and exposed in the mild asthma group. The geometric mean allergen concentrations, with the exception of bedroom Fel d 1, were greater in sensitized severe asthmatics than the sensitized mild asthmatics, which was significant for Der p 1 in bedroom samples and Can f 1 in bedroom and living room samples. These results support an association between the degrees of domestic allergen exposure in sensitized individuals and asthma severity.