The American house dust mite, Dermatophagoides farinae Hughes, is the most important factor of allergic diseases, such as atopic dermatitis, rhinitis, and asthma. The protein-denaturing activity of nerolidol (1), chrysin (2), and spathulenol (3) identified in the Brazilian propolis against D. farinae was evaluated using SDS-PAGE and dot-blot immunoassay. Results were compared with those of the currently available dust mite protein-denaturing agent tannic acid. SDS-PAGE showed that application of test compounds and tannic acid (100 μg each) caused complete disappearance of D. farinae protein bands. In a dot-blot immunoassay, test compounds and tannic acid (100 μg each) strongly inhibited the IgE-binding reactivity to D. farinae protein of a highly mite-sensitive asthmatic patient. The Brazilian propolis constituents described merit further study as potential dust mite-allergen denaturants for protection from humans from various diseases caused by house dust mites.