Effects of calorie restriction, high fat diet (20% corn oil) and the diets containing crude proteins prepared from the livers of rats which had been fed either a low casein diet or a threonine imbalanced diet for 37 days on fatty liver due to feeding a threonine imbalanced diet were examined 1) When food intake of rats in the imbalanced group (BM group) was restricted to the level of the B group (pair-feeding), there was no significant increase in the liver triglyceride. 2) Feeding the imbalanced diet with 20 90 fat also caused fatty liver, the extent of lipid accumulation being similar to that seen in the rat fed the ordinary 5% fat diet. 3) In the experiments using the crude liver proteins prepared from the rats which had been fed the control or imbalanced diet, no fatty liver was observed, though there were some increases in liver lipids compared with those of rats fed the usual low casein diet. 4) By feeding the high fat diet, percentage of docosahexaenoic acid (ω 3) in phosphatidylcholine and phosphatidylethanolamine decreased in the BM group and that of arachidonic acid in the latter increased. From these results, the involvement of the alternative factor(s), in addition to the increased calorie intake and hepatic lipogenesis, responsible for the development of this type of fatty liver is suggested.