To the Editor: —I have noted several queries inThe Journalas to the toxicity, if any, from the active immunization against diphtheria by periodic injections of toxin-antitoxin mixture. I have immunized a few thousand children during the last four years, without any definite reaction till recently. A 10 months old baby had received two injections of the toxin-antitoxin mixture at two week intervals, without any reaction other than the usual local redness at the site of the injection. About ten minutes after the third injection, which was twenty-eight days and fourteen days, respectively, after the first and second injections, the child developed hyperpnea lasting a few seconds, then dyspnea for only a very few seconds; it became moderately cyanotic for perhaps thirty seconds, and, finally, two or three minutes later, giant urticaria appeared on the face and neck, and spread rapidly over the chest, abdomen and lower extremities. However,