Acute fatty enlargement of the liver after the new-born period is comparatively infrequent. During the last year we have had the opportunity of seeing four cases, the infants all being under 1 year of age. In two of these cases the etiology for the liver condition was evident; one infant had ingested some insecticide paste which contained phosphorus; in the other arsenic was the toxic agent, demonstrated after a chemical examination of the organs. In the two remaining cases the etiology was unknown; their ages were 4½ months and 11½ months, respectively. Both children were almost entirely breast fed at the time of admission to the hospital. There was nothing characteristic in the clinical history. One child had had a convulsion five weeks previously; the other had had intermittent vomiting for the last two months. On physical examination these fairly well developed children were acutely ill with a moderate rise