Twenty-two dogs with allergic dermatitis, which are evaluated from physical findings, and 30 normal dogs were tested for this allergy using the immediate type-intradermal test with25 allergens, including house dust, red pine pollen, Japanese ceder pollen, ragweed pollen, wheat flour, cow's milk, whole eggs, egg yolks, egg whites, beef, pork, chicken, yeast, dog hair, cat hair, chicken feathers, sheep hair, cigarette smoke, kapok, Alternaria, Cladosporium, Aspergillus, Candida, Penicillium, and fleas, with both of the histamine phosphates diluted 1: 10, 000 as the positive control and 0.5% phenol-saline as the negative control. The tests were read 15 min after injection. According to fundamental study for standardization of criterion of the positive response, a positive reaction was determined when the diameter of the wheal at the injection site was larger than the median value between the positive and negative controls. Eleven of the 22 dogs with dermatitis were positive for fleas and one for both fleas and house dust. In 4 of the 30 normal dogs, 2 dogs werepositive for fleas and one for ragweed and another one for Candida. The histological examination showed marked perivascular infiltrations of basophils, mast cells and eosinophils in the positive site for flea allergen.