Objectives The aim of this study was to characterise the response of acute phase proteins (APPs) in cats seropositive for Dirofilaria immitis and to its endosymbiont bacterium Wolbachia. Methods The APPs serum amyloid A (SAA), haptoglobin (Hp) and ceruloplasmin (Cp) were measured in 25 seropositive cats and in 16 healthy seronegative cats. Results SAA and Cp concentrations were significantly higher in animals with D immitis seropositivity that exhibited clinical signs related to the disease, and Hp was elevated in all D immitis-seropositive animals. There was no significant correlation between APPs and D immitis or Wolbachia species antibody titres. Conclusions and relevance An association between feline seropositivity to D immitis and APP response was demonstrated. Increases in serum SAA and Cp concentrations were related to D immitis-associated clinical signs, whereas Hp increased in all seropositive animals.