Random-source dogs (n = 100) in Virginia and North Carolina were surveyed for the microfilariae of Dirofilaria immitis. Microscopic examination of fresh thin-films and modified Knott preparations were made. Dirofilaria immitis and Dipetalonema reconditum were found in 19% and 6% of the animals, respectively. There was no animal that harbored both species. Prevalence was significantly higher in North Carolina (28.6%) than in Virginia (13.6%) (P less than 0.025). Mean PCV was significantly lower (P less than 0.005) in infected vs noninfected animals.