It is not within the scope of this paper to review in detail the various toxic reactions which result from penicillin sensitivity, as this information is readily available in any of the namerous publications on the subject, but rather to discuss a few of the more salient factors which should be borne in mind when one is called on to use this drug. Many reactions to penicillin or to the toxic impurities contained in individual batches of the extract have been described in the literature. Among these pruritus, urticaria, vesicular and bullous dermatitis, chills, fever, headaches and gastrointestinal disturbances have been particularly emphasized. Fortunately, none of these reactions are of such severity as to jeopardize the life of the patient. Whether the sensitizing agent in a particular instance is the active principle of penicillin or other substance in commercial penicillin capable of producing sensitization is not known, although it is