Rats housed in group cages failed to develop the renal lesions of choline deficiency on a diet which was quite effective when the rats were in single cages. The addition of nicotinamide to this diet resulted in renal lesions even in the rats housed in group cages. While inositol exerted lipotropic activity in the liver, it appeared to increase slightly the incidence of hemorrhagic kidneys due to choline deficiency. A combination of inositol and tocopherol as well as a lipocaic preparation significantly decreased the incidence of such lesions while biotin and folic acid were without effect. Weanling rats on a diet containing 6% casein did not develop hemorrhagic kidneys until after 35 to 45 days, in contrast to rats receiving diets of higher protein concentration which develop such lesions in 6 to 10 days. While few adult rats developed renal lesions on choline deficient rations, choline deficient adult rats subjected to unilateral nephrectomy uniformly showed such lesions after 10 to 14 days, the period during which the remaining kidney hypertrophied. When adult nephrectomized rats were placed on a choline deficient regime 2 weeks after the operation, renal damage was observed in only one of 12 animals although they were continued on the diet for 6 weeks.