The aim of this study was to measure the levels of cat and dog allergen in homes of families that had either never kept pets or kept or had kept cats or dogs. From a small residential area outside Stockholm consisting of 250 houses with similar exteriors 70 homes were included. Dust samples were collected from mattresses and textile-covered floors. The levels of cat and dog allergen were analysed by ELISA. Fel dl was found in mattress dust in all 70 homes, median 0.5 μg/g [0.24–8.89 μg/g (quartiles)] and textile-covered floors 0.7 μg/g (0.20–2.52 μg/g). Can fl, was found in 98% of the collected samples, mattress dust 1.89μg/g (0.70–9.20 μg/g) and textile-covered floor dust 2.5 μg/g (1.04–2.72 μg/g). There was a positive correlation (p < 0.001) between allergen levels in dust from mattresses and textile-covered floors for both Fel dl(r = 0.68) and Can fl (r = 0.78). The highest levels of cat and dog allergen were found in homes with furred pets (p < 0.001). A significant (p < 0.001) difference was seen in the levels of Fel dl and Can f 1 between the homes of former pet-owners and homes without pets. In summary; cat and dog allergens are present in homes regardless of whether such animals live in the house or not. Mattresses seem to be an underestimated reservoir for pet allergens even in homes without pets. It is important to note that the homes of former pet owners have much lower levels of allergen than current pet owners.