81 dogs naturally infected with Leishmania infantum in the Isle of Elba, Italy, were treated with meglumine antimoniate (Glucantime). 36 of them (45.5%) were asymptomatic cases. 4-24 months after treatment the dogs were clinically and serologically examined; the recovery rates were 47.2% for asymptomatic cases, 33.3% for oligosymptomatic cases, and 11.1% for symptomatic cases. Furthermore, treatment had prevented the development of patent disease in 90% of non-recovered asymptomatic cases, whereas it had produced only slight improvement of clinical condition in patent dogs which were still infected after drug administration. Treatment with antimonial drugs is therefore recommended in canine leishmaniasis control if non-patent or sub-clinical forms of the disease are detected by seroepidemiological surveys.