In sensitized persons, patch tests with allergens may show a local reaction varying from a mild erythema to erythema with edema, papules, and vesicles. Such reactions are usually graded 1 to 4 plus depending upon the degree of reaction. Patch tests with many primary irritants may show somewhat similar local reactions. In some instances, however, the reactions are so severe as to produce ulcerations. These two commonly observed reaction types, however, do not appear to cover all forms of reactions that occur from patch tests.There exists still another type of patch test reaction which differs in many respects from the above mentioned. Sulzberger and Witten have called attention to a pustular type reaction which, it appears, has escaped general notice, and consequently has not had adequate work-up. These pustular patch test reactions are especially produced by certain salts of heavy metals and halogens. Usually, the pustules are small, measuring