Thirteen patients with a clinical diagnosis of pulmonary aspergillosis were treated with the anti-amoebic drug di-iodohydroxyquinoline, 1500-1800 mg/day orally, for 20 days. All were precipitin positive before treatment and all but one became negative after treatment. Sputum became negative in all of the 10 patients in whom it had been positive before treatment. Clinical improvement was marked in four patients, moderate in three, and slight in three, no change occurring in the remaining three. These results suggest that di-iodohydroxyquinoline may be of value in the treatment of pulmonary aspergillosis.