Summary 1. Eight patients with pulmonary infiltrations and eosinophilia are described. 2. Five of the cases were mild and corresponded to the original descriptionof Loeffler's syndrome. Three cases were chronic and the condition persisted for months. These cases correspond to the broader and more recent concept of Loeffler's syndrome. 3. Three patients were for a time mistakenly diagnosed as miliary tuberculosis because of the nature of the x-ray shadows and the presence of a positive tuberculin skin test. The importance of differentiating Loeffler's syndrome in patients with positive tuberculin is emphasized. 4. Disturbed liver function was found in the three patients with a chronic course. 5. In seven instances the pulmonary x-ray shadow cleared before the eosinophilecount in the peripheral blood returned to normal levels. 6. All of the patients survived. In seven patients intestinal parasitism was found. In the eighth patient, bacterial allergy associated with infected sinuses is suggested as the cause of the Loeffler's syndrome.