The effect of solidified benzyl benzoate (bb) foam and powder on concentrations of the major allergens of Dermatophagoides pteronyssinus (Der p I) and D. farinae (Der f I) in dust samples from mattresses and carpets in 22 households was investigated in a randomized, double-blind, placebo-controlled trial. All houses had been demonstrated to have significant (greater than or equal to 2000 ng/gm of dust) mite-allergen concentrations on mattresses. Dust samples were collected from mattresses and carpets before treatment and on days 10, 30, and 60 after the first treatment. There was a second application on day 10. Der p I and Der f I were determined by a sandwich-type ELISA with monoclonal noncross-reacting antibodies to Der p I and polyclonal monospecific antibodies to Der f I. There was a significant reduction of mite allergens in mattresses and carpets within both bb-treated and control groups, but only the results on carpets of the bb-treated group were significantly different from results of the control group on days 30 and 60 (p less than 0.05).