We hypothesized that (1) pPCT concentrations are significantly higher in dogs with bacterial sepsis than in dogs with non-infectious systemic inflammatory response syndrome (nSIRS) or healthy dogs, (2) pPCT decreases within the first 4 days of treatment in septic dogs with favorable clinical outcome, (3) initial pPCT concentrations are lower in dogs pretreated with antimicrobials compared to untreated dogs and (4) pPCT is superior to CRP, white blood cell (WBC) concentration and band neutrophil concentration to differentiate dogs with bacterial sepsis from dogs with nSIRS. The gene discussed is CRP; the disease is systemic inflammatory response syndrome.