The great advances made in the last few years in the treatment of disease by the use of anti-sera are marred by a few deaths from hypersensitiveness to horse serum. Individuals differ widely in their reactions to serum injections, so widely in fact, that thus far it is impossible to say how large a dose will be necessary to sensitize. Even the small dose administered in the diphtheria toxin-antoxin mixtures may result in, at least, skin sensitivity (1). At the present time, the intradermal test is the most common method used to determine sensitivity in the person who is to receive the serum injection. A small amount of horse serum is injected between the layers of the skin, and if the skin is sensitive, an urticarial wheal will develop at the site of the injection.