The incidence of canine visceral leishmaniasis (CVL) is increasing in the Mediterranean region. Many drugs have been tested for treatment of CVL, but little is known regarding their effect on test immune responses. In our study, three dogs naturally infected with Leishmania infantum and five dogs experimentally infected with the same strain, were treated with dimethasulfonate pentamidine (Lomidine) and the immune response evaluated before, and after, treatment. After the last injection, animals began to gain weight and the major clinical signs disappeared.