Clinical and immunological findings from 35 dogs infected with Leishmania braziliensis braziliensis are described. The majority of the dogs had ulcerated single lesions on the ears. Sera from all infected dogs showed detectable Leishmania-induced antibodies using an indirect fluorescent antibody test. Antimonial therapy resulted in prompt healing of the lesions in 80.9% of the animals followed by a significant reduction in the anti-Leishmania antibody titers. However, treatment follow-up showed recurrences at the site of the primary lesion in 42.8% of the cases. These data were correlated with a persistence of the parasite in clinically healed lesions as well as with a negative intradermal test (leishmanin-delayed type hypersensitivity) observed in all animals but one.