The distribution of vitamin B in the body of rats reared on diets containing different amounts of vitamin B was studied. The results show that in the body of the rat reared on a normal diet, diet B of this laboratory, there is ten times as much vitamin B per gram in the liver as in the muscle. Kidney is about one-half and brain is about one-third as rich per gram as liver. Heart is almost as rich as liver and nearly ten times as rich per gram as muscle. Blood, spleen, and lung, in the amounts fed, seemed to contain only traces of the vitamin. By comparing the growth of experimental animals which had been given tissue from animals fed for 1 month on a diet lacking vitamin B with the growth of experimental animals receiving tissue from animals kept for 1 month on a normal diet (diet B) to which had been added 2 per cent of brewers' yeast to augment the vitamin B content, it was found that the former animals, except for those receiving brain, lived no longer on an average than did the negative controls. This showed either a complete lack of vitamin B in the tissues of the depleted animals or too small an amount to be detected by this method. The animals receiving the brain tissues lived longer than did the negative controls, some even surviving the experimental period, but all lost weight rapidly. The experimental animals receiving the tissues of rats fed for 1 month on a diet containing extra yeast showed increased storage of vitamin B in some of their tissues. In the case of the experimental animals receiving muscle, liver, kidney and brain, there was an increase in growth of from 10 to 15 gm. over that made by the animals receiving tissue of rats reared on the normal diet. The experimental animals receiving lung lived an average of 12 days longer than did the experimental animals receiving the lung tissue of animals reared on the normal diet. Heart, spleen and blood showed no evidence of extra storage of vitamin B when the amount of vitamin B in the diet was increased. It has been shown, therefore, by these experiments that the amount of vitamin B in the body of the rat may be changed within certain limits by varying the amount of vitamin B in the diet.