Delta toxin, a hemolytic exocellular protein excreted by C. perfringens type C has been purified to homogeneity, assessed by polyacrylamide disc gel electrophoresis. Purification steps involved successively calcium phosphate gel formation in culture supernatant fluid, salting-out of unadsorbed material by ammonium sulfate to 50 % saturation, isoelectric focusing and gel filtration on Sephadex G75. Purified toxin appears as a basic protein occuring in two forms with isoelectric points of 8.8 and 9.4 as disclosed by isoelectric focusing. Molecular weight estimated by SDS-polyacrylamide disc gel electrophoresis was found to be close to 42,000 for the two forms. The lytic activity of delta toxin is inhibited by Ca++ and EDTA. The toxin is activated by short-term treatment with low concentration of trypsin.