The potency of vaccine against Cl. botulinum type C was tested comparatively in mice, guinea pigs and mink, using the test methods employed in the United States, Great Britain and Sweden. Additionally the capacity to withstand challenge to toxin in ferrets was investigated. All species of laboratory animals proved to be protected against high toxin doses. On the other hand the humoral antitoxin titer of the immunized animals was low after one injection. After a second injection or after challenge with toxin the titer increased considerably.