The occurrence of human pulmonary dirofilariasis maintains a relation with the prevalence of Dirofilaria immitis infection in the canine population. Several mosquito species are vectors of this nematode. Canine blood samples collected in Pingo d'Agua and União villages, Salvaterra municipality (Marajó Island, Pará), in June, 2004 (n = 34) and April, 2005 (N = 90) were analyzed. Parasitological and immunological (ELISA--kit SNAP(R) 3DX Biobrasil) diagnoses were compared following the examination of 34 samples. The prevalence in the population (N = 90) was evaluated by means of ELISA. ELISA revealed more positive samples (25/34; 73.5%) than thick smears (23/34, 67.6%) or Knott (21/34, 61.8%), but the differences were not significant (p > 0.05). The frequency of D. immitis infection was 58% in dogs ranging from 0-2 years old, whereas in older dogs it was 100%. The prevalence of canine dirofilariasis was high in Pingo d'Agua and Vila União (53.5%), indicating the risk of parasite transmission to the people in this area.