Abstract
Summary A review of the literature on occult filariasis and a consideration of the associated characteristic histological changes indicate that occult filariasis is caused by both human and animal filariae. It is assumed that the disease occurs only in persons who are hypersensitive to filarial antigen. There is accumulating evidence to show that many cases of tropical pulmonary eosinophilia are in fact cases of occult filariasis. It is proposed to use the term occult filariasis for those cases of tropical pulmonary eosinophilia in which a filarial infection is suspected or proved.