The prevalence of canine heartworm(Dirofilaria immitis) infection in 150 mixed-breed dogs (male: 54, female: 96) from February to December 1997 was investigated by using antigen test kit(ICT GOLD(TM) HW, Synbiotics, USA) based on immunochromatographic assay in Inchon city. Also, gross and histopathological findings of an antigen positive dog were carried out. The results were summarized as follows1. Four dogs were positive from 150 tested dogs(2.7%). They were all more than 2 years old and infection rates in male and outdoor dogs was higher than those in female and indoor, respectively. Species of infected dogs were Pug(2), German Sheperd(1) and Great-dane(1). 2. Regional infection rates were closely related with housing system in the city. 3. Pathological findings of antigen-positive dog was excessive enlargement, congestion and hemorrhage of lung and D immitis in heart and histologically hemosiderin, hypertrophy of pulmonary alveoli wall and irregular hypertrophy of pulmonary artery inner wall. Microfi-laria was observed in pulmonary artery and arteriole, ventricle and splenic artery.