Almost every physician who frequently has occasion to administer antitoxic serum has seen more or less serious symptoms follow the injection in individuals who months or even years previously have received serum. These symptoms usually develop within twenty-four hours, often in less time, and may be slight, consisting of one or several of the following: erythema, urticaria, swelling of lymph-glands, joint pains, fever, or they may be very grave, consisting of the above in an exaggerated form with profound collapse, albuminuria and bloody stools. It seems very desirable to be able to determine in advance those cases in which a second administration of serum will precipitate dangerous anaphylactic manifestations. In a recent paper Knox, Moss and Brown 1 described a local cutaneous anaphylactic reaction which indicates hypersensitiveness in rabbits to horse serum. Thinking that this test might give the desired information in the case of patients requiring a second injection