The resistance of cattle with varying serum-antitoxin titres was determined by per os challenge. The results proved that a solid immunity can be produced against C. botulinum toxins C₁ and D. The immune response of cattle to various quantities of C. botulinum C₁ and D toxoids, aluminum phosphate adsorbed and in water-in-oil emulsion was investigated. The response to antigen in watering oil emulsion was far superior to the other when they were used for primary and secondary stimuli. When cattle had been given a solid basic immunity with 2 injections of antigen in water-in-oil emulsion, essentially the same booster effect was obtained with antigen in water-in-oil emulsion and in aqueous solution. Only some of the animals injected intramuscularly with antigens in water-in-oil emulsion developed local lesions. These lesions were not large and their histological picture indicated a noticeable decline in severity within 20 weeks. A case is thus made out for the use of C. botulinum C₁ and D toxoids in water-in-oil emulsion for the primary and secondary stimuli and an aqueous solution of these antigens for any booster stimulus as an improved method of protecting cattle against botulism.