Approximately 424 000 persons received duck embryo rabies vaccine between 1958 and 1971, with the following serious reactions being voluntarily reported: 22 cases of anaphylaxis, 11 of abdominal pain associated with nausea and vomiting, 5 of cranial or peripheral neuropathy, 4 of transverse myelitis, 2 of nonfatal encephalopathy, 2 of fatal encephalitis, and 1 of thrombocytopenic purpura. The only reported deaths occurred in individuals who may have died of other causes—for example, rabies itself. To determine the true incidence of reactions to the vaccine, prospective studies were carried out: of 1679 persons receiving preexposure prophylaxis, 67% developed local skin reactions, 10%, constitutional symptoms, and 0.5%, anaphylaxis. Of 116 persons receiving postexposure therapy, 100% had local reactions, 33%, constitutional symptoms, and 0.9%, anaphylaxis. Thus, although duck embryo rabies vaccine is associated with a high incidence of minor reactions, it rarely causes serious difficulty and can be safely used in rabies prophylaxis.