During an outbreak of mucocutaneous leishmaniasis in the year of 1976, the authors examined 64 domestic animais of which 38 were dogs and 28 were cats. Out of the 38 dogs that were examined they found, through histopathologics tests, natural infection by mucocutaneous leishmaniasis in four of them (10.52%) which present ulcers with invasion of the muzzles'mucosas.