Brook, brown, and rainbow trout were fed diets containing various levels of thiamin, pantothenic acid, and riboflavin. After a period trout were killed and their livers analyzed for the vitamin content. The diet causing maximum storage was considered to be the tentative requirement of the trout. No difference was found between the requirement of three species of trout and no difference was found between the two temperatures at which the experiment was run. The tentative requirement for riboflavin was established at between 0.44 and 0.68, pantothenic acid between 0.97 and 1.25, and thiamin between 0.150 and 0.186 milligrams per kilogram of body weight per day. The maximum storage was found to be between 18 and 20 micrograms of pantothenic acid, 15 and 16 micrograms of riboflavin, and 3.5 and 4.5 micrograms of thiamin per gram of liver tissue. A difference was found between the two series with respect to the level of stored pantothenic acid and thiamin. This difference may be a function of age or size. The limitations of this type of study are discussed.