BACKGROUND Although cockroach allergen is an important indoor allergen in poor urban environments, no studies on the effectiveness of measures to reduce allergen levels in indoor environments have yet been published. METHODS As a model of home extermination, we studied cockroach allergen levels in an urban dormitory that was chronically infested with German cockroaches and that underwent semiannual extermination. Dust samples were collected from 18 bedrooms and 5 kitchens located in the dormitory and were analyzed for Bla g 2 using an immunoassay. RESULTS We detected allergen in almost every bedroom, with median levels ranging from 3.0 U/g (units/g) in settled dust on the bed, 4.0 U/g on the carpeted floor, and 2.8 U/g in closets. In the kitchen, we found somewhat higher levels, 10.8 U/g on the floor and 2.8 U/g in floor cabinets. Repeated measures of floor dust were similar (median 4.4 and 4.0 U/g) despite weekly vacuum cleaning. In the 2 weeks before extermination, median levels were 5.2 U/g and in the 2 weeks following extermination and regular vacuuming, median levels fell to 0.95 U/g. CONCLUSIONS We concluded that successful allergen abatement could be accomplished in cockroach infested indoor environments using routine extermination and vacuuming.