The results of skin and bronchial tests and of the radioallergosorbent test (RAST) with allergen extract preparations from two different producers were compared. Eleven allergic children were tested with dog allergens and, with one exception, with birch and timothy pollen allergens. Both types of allergen extract preparation were standardized with respect to their allergenic activity. A good correlation was found between the results of the clinical diagnostic tests and the results of RAST. RAST and skin testing were equally effective as a supplement to case history for predicting the presence or absence of clinical allergy to the particular allergens. A good agreement was obtained in the results with the two different extract preparations. It was concluded that different preparations of allergen extracts may be used interchangeably in the in vivo and the in vitro systems on condition that all extract preparations have been standardized with respect to biological allcrgenic activity.