Allergy to house dust mites (HDM) and domestic pets is a major cause of asthma.People in developed countries spend more than 90% of their time indoors.We have measured levels of HDM allergen Der pI and cat allergen Fel dI inpublic buildings and public transport. Dust samples were collected byvacuuming a 1 m2 area for 2 min from five schools, six hotels, fourcinemas, six pubs, three buses, two trains and 12 domestic householdswithout a cat. Der pI and Fel dI were assayed with monoclonal antibodiesin a two-site immunometric ELISA. Der pI concentration was significantlyhigher in the private homes than in comparable sites in public placesexcept for cinema seats (where high values were found) compared withdomestic sofas. Der pI > 2000 ng/g of fine dust was found in 30% of theupholstered seats, 9% having a concentration > 10,000 ng/g. Fel dIlevels were significantly higher in the dust from upholstered seats(geometric mean 14.88 micrograms/g) than in carpeted floors (geometricmean 0.73 micrograms/g), and in public places than in private homes. FeldI > 8 micrograms/g was found in 79% of the upholstered seats orfurniture sampled in public buildings or public transport. In conclusion,upholstered seats from public buildings and public transport constitute anallergen reservoir for continuous contamination of the indoor environmentwhich could compromise the effects of allergen avoidance employed athome.