We present serological evidence that Dirofilaria immitis was the causative agent of subcutaneous nodules in two patients. ELISA and enzyme-linked immunoblot analysis showed that the two human sera had a reactivity pattern similar to that of D. immitis rabbit immune serum. The reaction pattern of the human sera was very different to that of Dirofilaria repens rabbit immune serum. In the light of our findings, the traditional view that subcutaneous filarial nodules are due to D. repens has to be revised.