A 44-year-old man presented to the emergency room complaining of "not feeling well" for several days. He was treated with oxygen but became progressively worse with symptoms of adult respiratory distress syndrome. He died 4 hours after being admitted to the hospital. At autopsy, a histology of the lung showed diffuse alveolar damage with hyaline membrane formation. The slow-growing bacteria of Capnocytophaga species were considered in the differential diagnoses; and after several days, the organism that grew on chocolate agar was identified as Capnocytophaga canimorsus, a bacteria found in cats or dogs and that can be transmitted to people through bites, licking, scratching, or other types of exposure to the animal. Individuals who have had their spleens removed are particularly at risk for infection from this bacteria. This was the condition of the individual in the case study. It is important for emergency personnel and forensic pathologists to be aware of canine Capnocytophaga infections, particularly in patients with impaired immune systems and asplenia who show bites, scratches, or even superficial contact with the saliva of cats or dogs. It is rare for healthy persons to become infected with this bacteria. 1 figure and 16 references