The concentrations of haptoglobin, C-reactive protein and ceruloplasmin were measured in symptomatic and asymptomatic dogs naturally infected by Leishmania infantum, and in healthy uninfected dogs to determine the potential value of these proteins for the diagnosis and prognosis of leishmaniasis. The concentrations of the acute phase proteins were significantly higher in the dogs with leishmaniasis than in the control dogs, and the concentration of C-reactive protein was significantly higher in the symptomatic dogs than in the asymptomatic dogs. There were no correlations between the acute phase proteins and the gamma globulins, the albumin/globulin ratio or the titre of anti-leishmanial antibodies.