A 2.5-years-old female mongrel dog was routinely subcutaneously vaccinated. A few hours later mental dullness was noticed by the owner progressing into stupor the next day and resulting in a comatose state and death within 48 hours after vaccination. At post mortem examination, which was extended with histology and bacteriology, a necrotizing fasciitis and bacteremia caused by Streptococcus equi subsp. zooepidemicus were established. In the isolated Streptococcus strain four different superantigens were demonstrated that appeared to be able to produce exotoxins in vitro. Therefore, it is concluded that the minor skin trauma caused by vaccination enabled this strain to gain access to the subcutaneous tissue and to induce a necrotizing fasciitis. This process was complicated with a bacterial septicemia leading to death of the dog within 48 hours.