The authors carried out microscopic examination of blood smears of 1438 dogs infected with Leishmania infantum. Unusual findings of leishmaniosis associated with circulating parasitised cells are described in four dogs. Most of the dogs presented severe illness, with lethargy, dysorexia, emaciation and alterations of the haematological pattern (anaemia, thrombocytopenia, neutrophilia and monocytosis). In three cases, leishmaniosis was associated with ehrlichiosis. On examination of peripheral blood smears, Leishmania sp. amastigotes were observed both in various circulating leukocytes (neutrophil, monocyte, macrophage) and free. In conclusion, parasites can rarely be detected in blood smears (in 0.28% of the animals examined); thus, the time-consuming microscopic search for amastigotes can make only a weak contribution to the conventional diagnosis of canine leishmaniosis.