Highly purified Cl. perfringens type D epsilon prototoxin was prepared by ammonium sulphate precipitation and DEAE cellulose chromatography of culture filtrate of cultures of Cl. perfringens type D (Strain ET 468). Preparations of prototoxin were electrophoretically heterogeneous. The protein bands demonstrable in polyacrylamide gel electrophoresis were, however, all immunologically identical and toxic. The faster moving bands were shown to be degradation products of the main prototoxin band which was the slowest moving of the major bands. There was an inverse relationship between electrophoretic mobility and the activation ratio of these degradation products. The unde- graded prototoxin could be separated from its degradation products by CM cellulose chromatography but degradation appears to be a continual process and isolation of an absolutely pure product was not achieved.