Acute porphyria is a disease which has been recognized for many years and which has received considerable attention in the literature but which has been neglected in medical teaching, so that it is totally unfamiliar to many or most physicians. I1have made the suggestion that this disease is not as unusual as was formerly supposed and that with a more general knowledge of the subject more cases will be detected. My purpose in the present communication is to review the clinical aspects of the disease and to present 3 additional cases of unusual interest occurring in the same family which have been encountered during the past year. For a proper understanding of the disease, certain historical aspects of the problem are worth noting. In 1841 Scherer2described a red pigment formed by the action of strong sulfuric acid on hemoglobin. Although similar observations were made by Mulder,