Two raccoons, Procyon lotor, were exposed to Dirofilaria immitis by subcutaneous injection of infective third stage larvae obtained from experimentally-infected Aedes trivittatus. Nematodes were not recovered from either raccoon when examined at necropsy 223 and 254 days postexposure. Large numbers of adult D. immitis were found in six dogs used as controls. These data indicate that raccoons cannot support the development of D. immitis.