A 4.5 months old, previously healthy Danish girl was admitted to a paediatric department after six days of passive behaviour and weak suck. Over the next days she became increasingly weak, developed bilateral ptosis, the muscle stretch reflexes were lost, and mydriasis with slow pupillary responses was noted. Botulism was suspected and confirmed by testing of patient serum in a bioassay. The condition of the patient improved following administration of botulism antiserum. The clinical picture was suggestive of intestinal (infant) botulism. However, botulism acquired from consumption of food with preformed neurotoxin could not be excluded.