Room characteristics predicting indoor allergen exposure in suburban homes have not been clearly identified. To examine relationships between room characteristics and concentrations of indoor allergens in homes of suburban asthmatic patients. The homes of 339 asthmatic children ages 6 to 17 years were studied. Home inspections were conducted by a trained technician, and dust samples were analyzed for indoor allergen content. A high allergen concentration was defined as 8 microg (U)/g or more of fine dust. Infrequent sheet washing and wall-to-wall carpet were risk factors for high bedroom dust mite concentrations. Infrequent sheet washing was also a risk factor for high Fel d 1 concentrations. Food remains in the bedroom was a risk factor for high bedroom Bla g 1 levels, and exposed food, leaks, and dirty pots were all risk factors for high kitchen Bla g 1 levels. The combination of lack of mattress or pillow encasements, infrequent sheet washing, and carpeting was associated with a 24-fold increase in odds of a high dust mite concentration (odds ratio [OR], 24.1; 95% confidence interval [CI], 3.2-181.4). Among non-cat owners, the combination of stuffed toys on the bed, lack of mattress or pillow encasements, and infrequent sheet washing was associated with a 49-fold increase in odds of a high Fel d 1 level (OR, 49.4; 95% CI, 2.8-887.3). The combination of leaks, exposed food, and dirty pots was associated with a high kitchen Bla g 1 concentration (OR, 10.6; 95% CI, 2.8-40.5). Specific room characteristics predict high indoor allergen exposure among children with asthma, and a combination of these characteristics may further increase the risk of high allergen exposure.