Extracts of horse dander (HD) and horse hair and skin scrapings (HHSS) have been compared with respect to their content of proteins and carbohydrates. The protein content of HD is more than double that of HHSS, while the carbohydrate content is of the same order. SDS-PAGE and IEF, both combined with immunoblotting, and CIE/CRIE showed the IgE-binding ability of the proteins/glycoproteins present in the two extracts. SDS-PAGE/immunoblotting showed the presence of mainly the same IgE-binding bands in the two extracts. Nine were detected in HD, and seven in HHSS. Four of these were glycoproteins. The most important allergen was a glycoprotein with molecular mass of 27 kDa showing IgE-binding ability to the 16 patient sera available. Another important allergen with molecular mass of 67 kDa is probably horse albumin. IEF/immunoblotting showed the presence of a glycoprotein with IgE-binding ability at pH 3.2 in both extracts. Tandem CRIE showed that both extracts contained the same four allergens as major allergens. In addition, as we observed when analyzing both extracts in CRIE against 16 different patient sera, each extract contained allergens not present in the other extract. We may conclude from this investigation that commercial allergen extracts to be used in diagnosis and immunotherapy should include both horse dander and horse hair and skin scrapings in the starting material for the preparation of extracts. If not, allergens which may be of importance for some patients will be missing.