A botulinum toxin from ensiled poultry litter which caused a major outbreak of bovine botulism was characterised as type C1. The litter produced transient ataxia when fed to two experimental calves and the clinical signs were accompanied by a transient appearance of serum toxin. Type C1 toxin was demonstrated in muscle tissues which had been taken during the outbreak from an affected animal with high circulating serum toxin, and held frozen for seven months. Clostridium botulinum type C organisms were demonstrated in faeces from another affected animal and also in kidney tissue from a third animal. These observations have implications for the diagnosis and management of future outbreaks of botulism and for the potential health risk from the meat of affected animals.