Human pulmonary dirofilariosis usually appears as a solitary pulmonary nodule. A 22 kDa antigen from Dirofilaria immitis adult worms specifically recognized by three sera from individuals diagnosed with pulmonary dirofilariosis was identified by enzyme-linked-immunoelectrotransfer blot. This antigen was purified by elution from acrylamide gels and evaluated in enzyme-linked immunoassay using sera from 92 patients with pulmonary dirofilariosis and other pulmonary and parasitic diseases. Its use in the diagnosis of human pulmonary dirofilariosis should be considered.