In earlier days when diphtheria antitoxin was given in whole horse serum, serum sickness was rather common. Weaver,1 in a series of 692 cases, reported serum disease in 31.1 per cent. of those in which antitoxin injections were given. He2 later reported 27.1 per cent. of serum sickness in patients receiving the antitoxin refined according to Banzhaf's modification of Gibson's method, while Heinemann's method of further refinement gave serum reactions in only 8.4 per cent. of cases. Different lots of antitoxin vary in the reactions caused, but with the present refined antitoxin, there are probably not more than 10 per cent. of cases in any large series that would show any serum sickness. The majority of these are mild and consist of localized urticaria lasting a few hours, and do not cause much concern. The case reported here was of a severe type, and occasioned a great deal