Forty-four dogs naturally infected by Leishmania infantum were divided into two groups: 20 thrombocytopenic dogs with fewer than 150 × 109 platelets/I, and 24 non-thrombocytopenic dogs with more than 200 × 109 platelets/I. Ten clinically healthy dogs were used as controls. A haematological profile was obtained and the dogs' serum was used to assess the presence of platelet-binding IgM and IgG antibodies using a flow cytometry technique. Nineteen of the 20 thrombocytopenic dogs, and 13 of the 24 non-thrombocytopenic dogs had detectable levels of platelet-binding immunoglobulins, but none of the control dogs did so. The differences were significantly different for both IgM and IgG platelet-binding antibodies.