In 1940 in South India a new syndrome characterized by persistent hypereosinophilia, chronic cough, and pulmonary infiltration suggestive of miliary tuberculosis was described and referred to as eosinophile lung. Three years later, in West India, the syndrome was again described and was named tropical eosinophilia. With these reports a 25-year quest for the agent causing the new disease was begun. The search was brought to a conclusive stage, though not really ended, in 1966 when dead microfilariae undergoing destruction were demonstrated in the lungs of persons having no microfilariae in the blood and no other recognized sign of filariasis. At about mid-point in this search, a different syndrome called visceral larva migrans, also characterized by persistent hypereosinophilia, was described. As the cause of this disease was found to be larval nematodes in the tissues, an etiologic relationship with eosinophilic lung was suspected.