Random subjects of the canine population brought to the veterinary clinics on Gran Canaria Island for routine health care examinations or procedures were included in the survey. All dogs were 6 months old or older, and many breeds were represented. None of the dogs in the study received heartworm chemoprophylaxis or chemotherapy. The dogs were randomly selected by the veterinarians, and the samples were obtained by cephalic venipuncture and kept refrigerated until assayed in our laboratory. A record form was completed for each dog, giving pertinent identification, history and demographic data. Blood was remitted to our laboratory where a haemagglutination test Vetred Dirofilariaw, Rhoˆne Me´rieux. was used for serologic detection of D. immitis antigens.